<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//NLM//DTD JATS (Z39.96) Journal Publishing DTD v1.3 20210610//EN" "JATS-journalpublishing1-3-mathml3.dtd">
<article xml:lang="EN" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ali="http://www.niso.org/schemas/ali/1.0/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" dtd-version="1.3" article-type="research-article">
<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Public Health</journal-id>
<journal-title-group>
<journal-title>Frontiers in Public Health</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Public Health</abbrev-journal-title>
</journal-title-group>
<issn pub-type="epub">2296-2565</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.3389/fpubh.2026.1754972</article-id>
<article-version article-version-type="Version of Record" vocab="NISO-RP-8-2008"/>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Original Research</subject>
</subj-group>
</article-categories>
<title-group>
<article-title>Influence of comorbidities, geriatric syndromes, and frailty on mortality risk by discharge destination in older adults after acute hospitalization: a nationwide cohort study</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name><surname>Kim</surname> <given-names>Sunyoung</given-names></name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
<xref ref-type="aff" rid="aff2"><sup>2</sup></xref>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Writing &#x2013; original draft" vocab-term-identifier="https://credit.niso.org/contributor-roles/writing-original-draft/">Writing &#x2013; original draft</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Conceptualization" vocab-term-identifier="https://credit.niso.org/contributor-roles/conceptualization/">Conceptualization</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Visualization" vocab-term-identifier="https://credit.niso.org/contributor-roles/visualization/">Visualization</role>
<uri xlink:href="https://loop.frontiersin.org/people/2806030"/>
</contrib>
<contrib contrib-type="author">
<name><surname>Lee</surname> <given-names>Jae-ryun</given-names></name>
<xref ref-type="aff" rid="aff3"><sup>3</sup></xref>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Writing &#x2013; review &amp; editing" vocab-term-identifier="https://credit.niso.org/contributor-roles/writing-review-editing/">Writing &#x2013; review &#x00026; editing</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Data curation" vocab-term-identifier="https://credit.niso.org/contributor-roles/data-curation/">Data curation</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Formal analysis" vocab-term-identifier="https://credit.niso.org/contributor-roles/formal-analysis/">Formal analysis</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Investigation" vocab-term-identifier="https://credit.niso.org/contributor-roles/investigation/">Investigation</role>
</contrib>
<contrib contrib-type="author">
<name><surname>Kim</surname> <given-names>Kyeongeun</given-names></name>
<xref ref-type="aff" rid="aff2"><sup>2</sup></xref>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Data curation" vocab-term-identifier="https://credit.niso.org/contributor-roles/data-curation/">Data curation</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Formal analysis" vocab-term-identifier="https://credit.niso.org/contributor-roles/formal-analysis/">Formal analysis</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Validation" vocab-term-identifier="https://credit.niso.org/contributor-roles/validation/">Validation</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Writing &#x2013; review &amp; editing" vocab-term-identifier="https://credit.niso.org/contributor-roles/writing-review-editing/">Writing &#x2013; review &#x00026; editing</role>
</contrib>
<contrib contrib-type="author">
<name><surname>Park</surname> <given-names>Jungha</given-names></name>
<xref ref-type="aff" rid="aff1"><sup>1</sup></xref>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Data curation" vocab-term-identifier="https://credit.niso.org/contributor-roles/data-curation/">Data curation</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Investigation" vocab-term-identifier="https://credit.niso.org/contributor-roles/investigation/">Investigation</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Resources" vocab-term-identifier="https://credit.niso.org/contributor-roles/resources/">Resources</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Writing &#x2013; review &amp; editing" vocab-term-identifier="https://credit.niso.org/contributor-roles/writing-review-editing/">Writing &#x2013; review &#x00026; editing</role>
<uri xlink:href="https://loop.frontiersin.org/people/1973625"/>
</contrib>
<contrib contrib-type="author">
<name><surname>Lee</surname> <given-names>Keehyuck</given-names></name>
<xref ref-type="aff" rid="aff3"><sup>3</sup></xref>
<xref ref-type="aff" rid="aff4"><sup>4</sup></xref>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Data curation" vocab-term-identifier="https://credit.niso.org/contributor-roles/data-curation/">Data curation</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Formal analysis" vocab-term-identifier="https://credit.niso.org/contributor-roles/formal-analysis/">Formal analysis</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Investigation" vocab-term-identifier="https://credit.niso.org/contributor-roles/investigation/">Investigation</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Writing &#x2013; review &amp; editing" vocab-term-identifier="https://credit.niso.org/contributor-roles/writing-review-editing/">Writing &#x2013; review &#x00026; editing</role>
</contrib>
<contrib contrib-type="author">
<name><surname>Koo</surname> <given-names>Hye Yeon</given-names></name>
<xref ref-type="aff" rid="aff3"><sup>3</sup></xref>
<xref ref-type="aff" rid="aff4"><sup>4</sup></xref>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Data curation" vocab-term-identifier="https://credit.niso.org/contributor-roles/data-curation/">Data curation</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Writing &#x2013; review &amp; editing" vocab-term-identifier="https://credit.niso.org/contributor-roles/writing-review-editing/">Writing &#x2013; review &#x00026; editing</role>
<uri xlink:href="https://loop.frontiersin.org/people/2394255"/>
</contrib>
<contrib contrib-type="author">
<name><surname>Cho</surname> <given-names>Eunbyul</given-names></name>
<xref ref-type="aff" rid="aff5"><sup>5</sup></xref>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Validation" vocab-term-identifier="https://credit.niso.org/contributor-roles/validation/">Validation</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Visualization" vocab-term-identifier="https://credit.niso.org/contributor-roles/visualization/">Visualization</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Writing &#x2013; review &amp; editing" vocab-term-identifier="https://credit.niso.org/contributor-roles/writing-review-editing/">Writing &#x2013; review &#x00026; editing</role>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name><surname>Lee</surname> <given-names>Hyejin</given-names></name>
<xref ref-type="aff" rid="aff3"><sup>3</sup></xref>
<xref ref-type="aff" rid="aff4"><sup>4</sup></xref>
<xref ref-type="corresp" rid="c001"><sup>&#x0002A;</sup></xref>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Conceptualization" vocab-term-identifier="https://credit.niso.org/contributor-roles/conceptualization/">Conceptualization</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Supervision" vocab-term-identifier="https://credit.niso.org/contributor-roles/supervision/">Supervision</role>
<role vocab="credit" vocab-identifier="https://credit.niso.org/" vocab-term="Writing &#x2013; review &amp; editing" vocab-term-identifier="https://credit.niso.org/contributor-roles/writing-review-editing/">Writing &#x2013; review &#x00026; editing</role>
<uri xlink:href="https://loop.frontiersin.org/people/1487882"/>
</contrib>
</contrib-group>
<aff id="aff1"><label>1</label><institution>Department of Family Medicine, Kyung Hee University Medical Center, Kyung Hee University College of Medicine</institution>, <city>Seoul</city>, <country country="kr">Republic of Korea</country></aff>
<aff id="aff2"><label>2</label><institution>Center for Digital Health, Medical Science Research Institute, Kyung Hee University College of Medicine</institution>, <city>Seoul</city>, <country country="kr">Republic of Korea</country></aff>
<aff id="aff3"><label>3</label><institution>Department of Family Medicine, Seoul National University Bundang Hospital</institution>, <city>Seongnam</city>, <country country="kr">Republic of Korea</country></aff>
<aff id="aff4"><label>4</label><institution>Department of Family Medicine, Seoul National University</institution>, <city>Seoul</city>, <country country="kr">Republic of Korea</country></aff>
<aff id="aff5"><label>5</label><institution>Department of Family Medicine, Hallym University Dongtan Sacred Heart Hospital</institution>, <city>Hwaseong</city>, <country country="kr">Republic of Korea</country></aff>
<author-notes>
<corresp id="c001"><label>&#x0002A;</label>Correspondence: Hyejin Lee, <email xlink:href="mailto:jie2128@gmail.com">jie2128@gmail.com</email></corresp>
</author-notes>
<pub-date publication-format="electronic" date-type="pub" iso-8601-date="2026-02-27">
<day>27</day>
<month>02</month>
<year>2026</year>
</pub-date>
<pub-date publication-format="electronic" date-type="collection">
<year>2026</year>
</pub-date>
<volume>14</volume>
<elocation-id>1754972</elocation-id>
<history>
<date date-type="received">
<day>26</day>
<month>11</month>
<year>2025</year>
</date>
<date date-type="rev-recd">
<day>06</day>
<month>02</month>
<year>2026</year>
</date>
<date date-type="accepted">
<day>06</day>
<month>02</month>
<year>2026</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#x000A9; 2026 Kim, Lee, Kim, Park, Lee, Koo, Cho and Lee.</copyright-statement>
<copyright-year>2026</copyright-year>
<copyright-holder>Kim, Lee, Kim, Park, Lee, Koo, Cho and Lee</copyright-holder>
<license>
<ali:license_ref start_date="2026-02-27">https://creativecommons.org/licenses/by/4.0/</ali:license_ref>
<license-p>This is an open-access article distributed under the terms of the <ext-link ext-link-type="uri" xlink:href="https://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution License (CC BY)</ext-link>. The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</license-p>
</license>
</permissions>
<abstract>
<sec>
<title>Background</title>
<p>This study investigated its impact of discharge destination on mortality risk among older adults following acute hospital discharge, focusing on the effects of frailty, geriatric syndromes, and comorbidities.</p></sec>
<sec>
<title>Methods</title>
<p>Nationwide claims data from the South Korean National Health Insurance Service of individuals aged &#x02265;65 years who were discharged from acute care hospitals in 2017 were retrospectively analyzed, with participants followed for mortality outcomes over 4 years. Multivariable Cox proportional hazards models were used to estimate adjusted hazard ratios (aHR) for mortality according to discharge destination and geriatric status.</p></sec>
<sec>
<title>Results</title>
<p>This study included 1,115,556 participants (mean age, 75.5 years; 45.6% men). The most common discharge destination was home (76.5%), followed by tertiary/general hospitals (15.2%), long-term care hospitals (5.2%), hospitals (2.3%), and other facilities (0.8%). Patients discharged to long-term care hospitals were older, had a higher comorbidity burden, and more frequently had disabilities or geriatric syndromes than their counterparts. Mortality risk was significantly higher among those discharged to tertiary/general hospitals (aHR 1.806, 95% CI: 1.793&#x02013;1.820), general hospitals (aHR 1.480, 95% CI: 1.453&#x02013;1.507), and long-term care hospitals (aHR 2.922, 95% CI: 2.892&#x02013;2.952) than among those discharged to home. Higher Charlson comorbidity index (&#x02265;3), more geriatric syndromes, and severe frailty were all independently associated with increased mortality risk.</p></sec>
<sec>
<title>Conclusion</title>
<p>Discharge destination, frailty, geriatric syndromes, and comorbidities independently and interactively influenced the mortality risk in older adults after acute hospitalization. Tailored post-discharge management strategies are necessary, particularly for patients with frailty and multimorbidity in community settings.</p></sec></abstract>
<kwd-group>
<kwd>comorbidities</kwd>
<kwd>frailty</kwd>
<kwd>geriatric syndrome</kwd>
<kwd>older (diseased) population</kwd>
<kwd>post-discharge</kwd>
</kwd-group>
<funding-group>
<funding-statement>The author(s) declared that financial support was not received for this work and/or its publication.</funding-statement>
</funding-group>
<counts>
<fig-count count="1"/>
<table-count count="4"/>
<equation-count count="0"/>
<ref-count count="38"/>
<page-count count="13"/>
<word-count count="8561"/>
</counts>
<custom-meta-group>
<custom-meta>
<meta-name>section-at-acceptance</meta-name>
<meta-value>Aging and Public Health</meta-value>
</custom-meta>
</custom-meta-group>
</article-meta>
</front>
<body>
<sec id="s1">
<label>1</label>
<title>Background</title>
<p>The global trend of an aging population has increased, and South Korea is experiencing one of the most rapid demographic transitions worldwide. As of 2025, individuals aged &#x02265;65 years constitute &#x0003E;20% of the total population, and this proportion will reach 40.1% by 2050 (<xref ref-type="bibr" rid="B1">1</xref>). Particularly notable is the sharp increase in the population aged &#x02265;75 years, which poses substantial challenges to the healthcare and social welfare systems (<xref ref-type="bibr" rid="B2">2</xref>, <xref ref-type="bibr" rid="B3">3</xref>).</p>
<p>Population aging is reshaping healthcare utilization patterns, especially in the context of acute care hospitalization and post-discharge management (<xref ref-type="bibr" rid="B4">4</xref>, <xref ref-type="bibr" rid="B5">5</xref>). The environment in which older adults are discharged following an acute hospital stay, whether at home, a rehabilitation hospital, or a long-term care facility, has emerged as a critical public health concern, significantly influencing both survival and quality of life (<xref ref-type="bibr" rid="B6">6</xref>&#x02013;<xref ref-type="bibr" rid="B8">8</xref>). Studies based on U.S. Medicare data have demonstrated that the 1 year mortality rate for patients discharged to nursing facilities 64%, compared to 11% for those discharged to home, underscoring the crucial role of post-discharge care environments in determining patient outcomes (<xref ref-type="bibr" rid="B9">9</xref>). Other studies have also demonstrated significant differences in 1-year mortality, readmission rates, and quality of life according to discharge destination (home, inpatient rehabilitation facility, or nursing home) after stroke (<xref ref-type="bibr" rid="B10">10</xref>).</p>
<p>Comorbidities, geriatric syndromes, and frailty are interrelated factors that profoundly affect health outcomes in older adults (<xref ref-type="bibr" rid="B11">11</xref>). Comorbidities are defined as co-occurring, etiologically independent chronic health conditions and are considered important predictors of survival, poor functional status, reduced quality of life, the possibility of a higher risk of adverse events in response to medication, and greater use of healthcare services (<xref ref-type="bibr" rid="B12">12</xref>, <xref ref-type="bibr" rid="B13">13</xref>). Frailty, characterized by increased vulnerability to stressors, such as falls, delirium, and malnutrition, is associated with more than double the 1-year mortality rate compared with its counterparts (51% vs. 25%) (<xref ref-type="bibr" rid="B14">14</xref>). Geriatric syndromes, including functional impairment and cognitive decline, are significant predictors of mortality, particularly when present with multiple comorbid conditions (<xref ref-type="bibr" rid="B15">15</xref>). The coexistence of multiple geriatric syndromes and comorbidities exponentially increases the mortality risk, highlighting the complex interplay between these factors (<xref ref-type="bibr" rid="B16">16</xref>). A comprehensive understanding of individual geriatric conditions and their interactions is crucial for improving prognostic outcomes and developing tailored interventions for vulnerable older adults (<xref ref-type="bibr" rid="B17">17</xref>).</p>
<p>In clinical practice, this multidimensional vulnerability most commonly manifests through the co-occurrence of multimorbidity, geriatric syndromes, and frailty, which together shape health trajectories during acute hospitalization and the post-discharge period. However, much of the existing evidence has been derived from single-center or regionally restricted cohorts and has typically examined discharge destination, frailty, comorbidity burden, or geriatric syndromes as isolated predictors (<xref ref-type="bibr" rid="B18">18</xref>&#x02013;<xref ref-type="bibr" rid="B20">20</xref>). Consequently, the population-level prognostic impact of their combined and interactive effects on post-discharge mortality remains insufficiently characterized. To address this gap, we analyze nationwide data from more than 1.1 million older adults to quantify how discharge destination interacts with frailty, geriatric syndromes, and comorbidity burden in determining mortality risk after hospitalization, thereby moving beyond discharge destination alone as a proxy for risk and better capturing multidimensional vulnerability in older patients.</p>
<p>Hence, the present study utilized nationwide big data from South Korea to analyze the relationships among discharge destination, comorbidities, geriatric syndromes, and frailty and to investigate their effects on mortality risk. This study aimed to provide evidence to optimize post-discharge management strategies and improve outcomes for vulnerable older patients.</p></sec>
<sec id="s2">
<label>2</label>
<title>Methods</title>
<sec>
<label>2.1</label>
<title>Data source and study population</title>
<p>This retrospective cohort study used population-based data from the National Health Insurance Service (NHIS) of South Korea. The NHIS is mandatory and covers approximately 97% of the South Korean population. The medical expenses of the remaining 3% of the population are fully covered through the government&#x00027;s Medical Aid programs. NHIS beneficiaries are responsible for approximately 20%&#x02212;30% of their out-of-pocket medical expenses, whereas Medical Aid recipients have no out-of-pocket payments. Healthcare providers submit claims for both NHIS beneficiaries and Medical Aid recipients to the NHIS, resulting in the near-complete integration of patient healthcare information within the NHIS database. This database is a comprehensive resource that encompasses healthcare utilization patterns, diagnostic information, and prescription drug details (<xref ref-type="bibr" rid="B21">21</xref>). This study was approved by the Institutional Review Board of Seoul National University Bundang Hospital (X-2406-904-901). The requirement for informed consent was waived owing to the retrospective study design.</p>
<p>To evaluate the impact of frailty on healthcare utilization and mortality, a retrospective cohort was constructed using 4 years of NHIS data from 2017 to 2020. The year 2017 was selected as the baseline period. Among the 1,137,491 individuals aged &#x02265;65 years who were discharged at least once from acute care hospitals (tertiary or general hospitals) between January 1 and December 31, 2017, those with missing data on key variables (<italic>n</italic> = 16,562), or those with unclear discharge destinations (<italic>n</italic> = 5,373) were excluded. Consequently, comorbidities, geriatric syndromes, and frailty were comprehensively assessed for the final study population of 1,115,556 individuals. Subsequently, mortality and healthcare utilization were tracked for 3 years (2018&#x02013;2020) according to comorbidities, geriatric syndromes, and frailty status.</p></sec>
<sec>
<label>2.2</label>
<title>Definition of variables</title>
<p>Comorbidities were assessed using the Charlson comorbidity index (CCI), calculated from diagnostic information recorded during the baseline period, in accordance with the validated ICD-10 coding algorithm (<xref ref-type="supplementary-material" rid="SM1">Supplementary Table 1-1</xref>) (<xref ref-type="bibr" rid="B22">22</xref>). Geriatric syndromes were identified using claims data from the National Health Insurance Service (NHIS) database, based on predefined ICD-10 diagnostic codes. The syndromes included delirium (F05, F05.0, F05.1, F05.8, F05.9), pressure ulcers (L89), incontinence (N39.3, N39.4, F98.1, F98.5, R15, R32), and osteoporosis-related fractures (S72.0, S52.5, S22-32), consistent with previously published NHIS-based studies (<xref ref-type="bibr" rid="B23">23</xref>). Frailty was evaluated using the multimorbidity frailty index (mFI), a 38-item deficit accumulation measure constructed from ICD-10 diagnostic codes, following the standardized approach originally proposed and subsequently validated in large population-based studies (<xref ref-type="supplementary-material" rid="SM1">Supplementary Table 1-2</xref>) (<xref ref-type="bibr" rid="B24">24</xref>). This ICD-10&#x02013;based mFI has been extensively applied and validated in analyses using the NHIS database, demonstrating good construct validity through consistent associations with mortality, healthcare utilization, and adverse health outcomes in older adults (<xref ref-type="bibr" rid="B25">25</xref>, <xref ref-type="bibr" rid="B26">26</xref>).</p>
<p>Each deficit was coded as present or absent, and the mFI score was calculated as the ratio of accumulated deficits to the total number of possible deficits, yielding a continuous score ranging from 0 to 1. Participants were categorized into four frailty groups&#x02014;fit, mildly frail, moderately frail, and severely frail&#x02014;according to established cut-off values used in prior validation studies.</p></sec>
<sec>
<label>2.3</label>
<title>Outcome of interest</title>
<p>Discharge destinations following acute hospitalization among study participants were assessed using 2017 data. Discharge destination was defined as the facility where the patient was admitted within 1 month of discharge. If no subsequent admissions occurred, the patient was assumed to have been discharged. Admissions to facilities, such as traditional medicine clinics or public health centers, were classified as &#x0201C;other&#x0201D; discharge destinations. Discharge destinations were categorized as tertiary/general hospitals, hospitals, long-term care hospitals (LTCH), home, and other facilities.</p>
<p>Healthcare utilization in South Korea is categorized into emergency, outpatient (OPD), and inpatient services, serving as comprehensive indicators of overall healthcare patterns. Each service type is analyzed based on distinct claim data submitted separately, reflecting the structured approach to healthcare delivery and resource allocation. This classification facilitates systematic analysis and policy development within the Korean healthcare system (<xref ref-type="bibr" rid="B27">27</xref>&#x02013;<xref ref-type="bibr" rid="B29">29</xref>).</p>
<p>The outcome of interest was the all-cause mortality. Participants were followed up from January 1, 2018 until the date of death or the last available date in the database (December 31, 2020), whichever occurred first.</p></sec>
<sec>
<label>2.4</label>
<title>Statistical analysis</title>
<p>Descriptive analysis was performed to summarize baseline characteristics, discharge destinations, and utilization by comorbidities, geriatric syndrome, and frailty status in 2017. Continuous variables in the text and tables are presented as means &#x000B1; standard deviations (SDs), whereas categorical variables are reported as percentages.</p>
<p>Cox proportional hazards models were used to evaluate the association between discharge destination and all-cause mortality, stratified by comorbidity, geriatric syndrome, and frailty status, while adjusting for age, sex, income, region, and disability. Adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) were determined. All statistical analyses were conducted using the SAS software (version 9.4; SAS Institute, Cary, NC, USA).</p></sec></sec>
<sec sec-type="results" id="s3">
<label>3</label>
<title>Results</title>
<sec>
<label>3.1</label>
<title>General characteristics</title>
<p>The study included 1,115,556 participants with a mean age of 75.5 years (SD = 7.13). Among them, 52.8% were aged &#x02265;75 years, and 45.6% were men. The most common discharge destination was home (853,041 patients; 76.5%), followed by tertiary or general hospitals (15.2%), long-term care hospitals (5.2%), hospitals (2.3%), and other facilities (0.8%) (<xref ref-type="fig" rid="F1">Figure 1</xref>).</p>
<fig position="float" id="F1">
<label>Figure 1</label>
<caption><p>Flow chart.</p></caption>
<graphic mimetype="image" mime-subtype="tiff" xlink:href="fpubh-14-1754972-g0001.tif">
<alt-text content-type="machine-generated">Flowchart describing study design for older adults discharged from acute care hospitals in 2017. Exclusions for missing or unclear data are shown, followed by analysis of 1,115,556 subjects. Discharge destinations, comorbidities, geriatric syndrome, and frailty are evaluated during a one-year baseline period. Subjects transition from acute hospital to tertiary/general hospital, hospital, long-term care hospital, or home, with a three-year follow-up tracking mortality as the endpoint. Dates for study start, follow-up, and end are included.</alt-text>
</graphic>
</fig>
<p>Geriatric syndromes were observed in 289,450 participants (25.9%), with osteoporosis-related fractures (104,315; 9.4%) and urinary incontinence (170,154; 15.3%) being the most prevalent. The mean CCI score was 4.35 (SD = 2.83), and the majority of participants (731,594; 65.6%) had a CCI score of &#x02265;3. The mean mFI was 0.11 (SD = 0.1), with 279,017 individuals (25%) classified in the severe frailty group (<xref ref-type="table" rid="T1">Table 1</xref>).</p>
<table-wrap position="float" id="T1">
<label>Table 1</label>
<caption><p>Baseline characteristics.</p></caption>
<table frame="box" rules="all">
<thead>
<tr>
<th valign="top" align="left"><bold>Variables</bold></th>
<th valign="top" align="center" colspan="2">Total</th>
<th valign="top" align="center" colspan="2">Alive</th>
<th valign="top" align="center" colspan="2">Died</th>
<th valign="top" align="center"><bold><italic>p-value</italic></bold></th>
</tr>
<tr>
<th/>
<th valign="top" align="center"><italic><bold>N</bold></italic></th>
<th valign="top" align="center"><bold>%</bold></th>
<th valign="top" align="center"><italic><bold>N</bold></italic></th>
<th valign="top" align="center"><bold>%</bold></th>
<th valign="top" align="center"><italic><bold>N</bold></italic></th>
<th valign="top" align="center"><bold>%</bold></th>
<th/>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">Total</td>
<td valign="top" align="center">1,115,556</td>
<td valign="top" align="center">100.0</td>
<td valign="top" align="center">694,736</td>
<td valign="top" align="center">100.0</td>
<td valign="top" align="center">420,812</td>
<td valign="top" align="center">100.0</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="7"><bold>Sex</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">Men</td>
<td valign="top" align="center">508,504</td>
<td valign="top" align="center">45.6</td>
<td valign="top" align="center">290,340</td>
<td valign="top" align="center">41.8</td>
<td valign="top" align="center">218,162</td>
<td valign="top" align="center">51.8</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Women</td>
<td valign="top" align="center">607,052</td>
<td valign="top" align="center">54.4</td>
<td valign="top" align="center">404,396</td>
<td valign="top" align="center">58.2</td>
<td valign="top" align="center">202,650</td>
<td valign="top" align="center">48.2</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Age (years)</td>
<td valign="top" align="center">75.5</td>
<td valign="top" align="center">7.1</td>
<td valign="top" align="center">73.4</td>
<td valign="top" align="center">6.1</td>
<td valign="top" align="center">79.1</td>
<td valign="top" align="center">7.3</td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">65&#x02013;74</td>
<td valign="top" align="center">526,230</td>
<td valign="top" align="center">47.2</td>
<td valign="top" align="center">412,244</td>
<td valign="top" align="center">59.3</td>
<td valign="top" align="center">113,986</td>
<td valign="top" align="center">27.1</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">&#x02265;75</td>
<td valign="top" align="center">589,326</td>
<td valign="top" align="center">52.8</td>
<td valign="top" align="center">282,492</td>
<td valign="top" align="center">40.7</td>
<td valign="top" align="center">306,826</td>
<td valign="top" align="center">72.9</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="7"><bold>Income</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">1st (highest)</td>
<td valign="top" align="center">399,722</td>
<td valign="top" align="center">35.8</td>
<td valign="top" align="center">251,259</td>
<td valign="top" align="center">36.2</td>
<td valign="top" align="center">148,458</td>
<td valign="top" align="center">35.3</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">2nd</td>
<td valign="top" align="center">215,706</td>
<td valign="top" align="center">19.3</td>
<td valign="top" align="center">140,621</td>
<td valign="top" align="center">20.2</td>
<td valign="top" align="center">75,084</td>
<td valign="top" align="center">17.8</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">3rd</td>
<td valign="top" align="center">139,429</td>
<td valign="top" align="center">12.5</td>
<td valign="top" align="center">88,697</td>
<td valign="top" align="center">12.8</td>
<td valign="top" align="center">50,732</td>
<td valign="top" align="center">12.1</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">4th</td>
<td valign="top" align="center">107,852</td>
<td valign="top" align="center">9.7</td>
<td valign="top" align="center">68,990</td>
<td valign="top" align="center">9.9</td>
<td valign="top" align="center">38,862</td>
<td valign="top" align="center">9.2</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">5th (lowest)</td>
<td valign="top" align="center">252,847</td>
<td valign="top" align="center">22.7</td>
<td valign="top" align="center">145,169</td>
<td valign="top" align="center">20.9</td>
<td valign="top" align="center">107,676</td>
<td valign="top" align="center">25.6</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="7"><bold>Region</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">Seoul metropolitan area</td>
<td valign="top" align="center">459,144</td>
<td valign="top" align="center">41.2</td>
<td valign="top" align="center">288,302</td>
<td valign="top" align="center">41.5</td>
<td valign="top" align="center">170,837</td>
<td valign="top" align="center">40.6</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Metropolitan cities</td>
<td valign="top" align="center">203,963</td>
<td valign="top" align="center">18.3</td>
<td valign="top" align="center">129,636</td>
<td valign="top" align="center">18.7</td>
<td valign="top" align="center">74,326</td>
<td valign="top" align="center">17.7</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Other areas</td>
<td valign="top" align="center">452,449</td>
<td valign="top" align="center">40.6</td>
<td valign="top" align="center">276,798</td>
<td valign="top" align="center">39.8</td>
<td valign="top" align="center">175,649</td>
<td valign="top" align="center">41.7</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="7"><bold>Disability</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">No</td>
<td valign="top" align="center">864,679</td>
<td valign="top" align="center">77.5</td>
<td valign="top" align="center">564,399</td>
<td valign="top" align="center">81.2</td>
<td valign="top" align="center">300,276</td>
<td valign="top" align="center">71.4</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Yes</td>
<td valign="top" align="center">250,877</td>
<td valign="top" align="center">22.5</td>
<td valign="top" align="center">130,337</td>
<td valign="top" align="center">18.8</td>
<td valign="top" align="center">120,536</td>
<td valign="top" align="center">28.6</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="7"><bold>Discharge destination</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">Tertiary and general hospitals</td>
<td valign="top" align="center">169,660</td>
<td valign="top" align="center">15.2</td>
<td valign="top" align="center">80,908</td>
<td valign="top" align="center">11.6</td>
<td valign="top" align="center">88,751</td>
<td valign="top" align="center">21.1</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Hospital</td>
<td valign="top" align="center">25,564</td>
<td valign="top" align="center">2.3</td>
<td valign="top" align="center">13,676</td>
<td valign="top" align="center">2.0</td>
<td valign="top" align="center">11,888</td>
<td valign="top" align="center">2.8</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Long-term care hospital</td>
<td valign="top" align="center">57,859</td>
<td valign="top" align="center">5.2</td>
<td valign="top" align="center">12,900</td>
<td valign="top" align="center">1.9</td>
<td valign="top" align="center">44,958</td>
<td valign="top" align="center">10.7</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Home</td>
<td valign="top" align="center">853,041</td>
<td valign="top" align="center">76.5</td>
<td valign="top" align="center">580,377</td>
<td valign="top" align="center">83.5</td>
<td valign="top" align="center">272,658</td>
<td valign="top" align="center">64.8</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Others</td>
<td valign="top" align="center">9,432</td>
<td valign="top" align="center">0.8</td>
<td valign="top" align="center">6,875</td>
<td valign="top" align="center">1.0</td>
<td valign="top" align="center">2,557</td>
<td valign="top" align="center">0.6</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Charlson comorbidity index</td>
<td valign="top" align="center">4.34800667</td>
<td valign="top" align="center">2.8</td>
<td valign="top" align="center">3.65574212</td>
<td valign="top" align="center">2.3</td>
<td valign="top" align="center">5.41773973</td>
<td valign="top" align="center">3.2</td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">&#x000A0;0</td>
<td valign="top" align="center">70,122</td>
<td valign="top" align="center">6.3</td>
<td valign="top" align="center">60,049</td>
<td valign="top" align="center">8.6</td>
<td valign="top" align="center">10,073</td>
<td valign="top" align="center">2.4</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">&#x000A0;1&#x02013;2</td>
<td valign="top" align="center">313,840</td>
<td valign="top" align="center">28.1</td>
<td valign="top" align="center">238,011</td>
<td valign="top" align="center">34.3</td>
<td valign="top" align="center">75,826</td>
<td valign="top" align="center">18.0</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">&#x000A0;&#x02265;3</td>
<td valign="top" align="center">731,594</td>
<td valign="top" align="center">65.6</td>
<td valign="top" align="center">396,676</td>
<td valign="top" align="center">57.1</td>
<td valign="top" align="center">334,913</td>
<td valign="top" align="center">79.6</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="7"><bold>Geriatric syndrome (number)</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">0</td>
<td valign="top" align="center">826,098</td>
<td valign="top" align="center">74.1</td>
<td valign="top" align="center">547,986</td>
<td valign="top" align="center">78.9</td>
<td valign="top" align="center">278,112</td>
<td valign="top" align="center">66.1</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">1</td>
<td valign="top" align="center">245,996</td>
<td valign="top" align="center">22.1</td>
<td valign="top" align="center">132,391</td>
<td valign="top" align="center">19.1</td>
<td valign="top" align="center">113,605</td>
<td valign="top" align="center">27.0</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">2</td>
<td valign="top" align="center">38,981</td>
<td valign="top" align="center">3.5</td>
<td valign="top" align="center">13,395</td>
<td valign="top" align="center">1.9</td>
<td valign="top" align="center">25,586</td>
<td valign="top" align="center">6.1</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">&#x02265;3</td>
<td valign="top" align="center">4,473</td>
<td valign="top" align="center">0.4</td>
<td valign="top" align="center">964</td>
<td valign="top" align="center">0.1</td>
<td valign="top" align="center">3,509</td>
<td valign="top" align="center">0.8</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="7"><bold>mFI</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">Fit</td>
<td valign="top" align="center">143,121</td>
<td valign="top" align="center">12.8</td>
<td valign="top" align="center">100,695</td>
<td valign="top" align="center">14.5</td>
<td valign="top" align="center">42,421</td>
<td valign="top" align="center">10.1</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Mild frail</td>
<td valign="top" align="center">361,965</td>
<td valign="top" align="center">32.4</td>
<td valign="top" align="center">239,534</td>
<td valign="top" align="center">34.5</td>
<td valign="top" align="center">122,430</td>
<td valign="top" align="center">29.1</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Moderate frail</td>
<td valign="top" align="center">331,453</td>
<td valign="top" align="center">29.7</td>
<td valign="top" align="center">202,618</td>
<td valign="top" align="center">29.2</td>
<td valign="top" align="center">128,834</td>
<td valign="top" align="center">30.6</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Severe frail</td>
<td valign="top" align="center">279,017</td>
<td valign="top" align="center">25.0</td>
<td valign="top" align="center">151,889</td>
<td valign="top" align="center">21.9</td>
<td valign="top" align="center">127,127</td>
<td valign="top" align="center">30.2</td>
<td/>
</tr></tbody>
</table>
</table-wrap></sec>
<sec>
<label>3.2</label>
<title>Characteristics depending on discharge destination</title>
<p>The mean age was highest among patients discharged to long-term care hospitals (80.70 years), followed by general hospitals (76.19 years), tertiary and general hospitals (75.80 years), and home (75.14 years) (<italic>p</italic> &#x0003C; 0.001). Regarding income level, in the highest income quintile (1st quintile), the proportion of patients discharged to tertiary/general hospitals (36.2%) and other facilities (36.3%) was higher. By contrast, among those in the lowest income quintile (5th quintile), discharge to long-term care hospitals was most common (29.8%) (<italic>p</italic> &#x0003C; 0.001).</p>
<p>In terms of comorbidity status, the mean CCI was highest for patients discharged to LTCHs (5.19 &#x000B1; 1.23), followed by general hospitals (5.12 &#x000B1; 1.15), tertiary/general hospitals (5.53 &#x000B1; 1.30), and home (4.02 &#x000B1; 1.05). Among patients with disabilities, 32.6% were discharged to LTCHs, which was significantly higher than for other discharge destinations (<italic>p</italic> &#x0003C; 0.001). According to discharge destinations by primary diagnosis, LTCHs had a higher proportion of patients with stroke (23.2%) and dementia (24.2%) than the other destinations. Meanwhile, patients with cancer were most frequently discharged to tertiary/general hospitals (23.4%) (<italic>p</italic> &#x0003C; 0.001).</p>
<p>Among patients with geriatric syndromes, discharge to LTCHs was the most common (47.8%), whereas discharge to home was the least common (23.3%). Among those with geriatric syndromes, 15.2% of patients with pressure ulcers and 5.2% of those with delirium were discharged to LTCHs (<italic>p</italic> &#x0003C; 0.001). Patients with severe frailty were most frequently discharged to general hospitals (36.7%) and least frequently discharged to home (23.3%) (<italic>p</italic> &#x0003C; 0.001; <xref ref-type="table" rid="T2">Table 2</xref>).</p>
<table-wrap position="float" id="T2">
<label>Table 2</label>
<caption><p>Characteristics of discharge destinations for patients discharged from acute care hospitals.</p></caption>
<table frame="box" rules="all">
<thead>
<tr>
<th valign="top" align="left"><bold>Variables</bold></th>
<th valign="top" align="center" colspan="10">Discharge destination, <italic><bold>N</bold></italic> (%)</th>
<th valign="top" align="center"><bold><italic>p-value</italic></bold></th>
</tr>
<tr>
<th/>
<th valign="top" align="center" colspan="2">Tertiary/general hospitals (<italic>n</italic> = 169,660)</th>
<th valign="top" align="center" colspan="2">Hospital (<italic>n</italic> = 25,564)</th>
<th valign="top" align="center" colspan="2">Long-term care hospital (<italic>n</italic> = 57,859)</th>
<th valign="top" align="center" colspan="2">Home (<italic>n</italic> = 853 041)</th>
<th valign="top" align="center" colspan="2">Others (<italic>n</italic> = 9,432)</th>
<th/>
</tr>
<tr>
<th/>
<th valign="top" align="center"><italic><bold>N</bold></italic></th>
<th valign="top" align="center"><bold>%</bold></th>
<th valign="top" align="center"><italic><bold>N</bold></italic></th>
<th valign="top" align="center"><bold>%</bold></th>
<th valign="top" align="center"><italic><bold>N</bold></italic></th>
<th valign="top" align="center"><bold>%</bold></th>
<th valign="top" align="center"><italic><bold>N</bold></italic></th>
<th valign="top" align="center"><bold>%</bold></th>
<th valign="top" align="center"><italic><bold>N</bold></italic></th>
<th valign="top" align="center"><bold>%</bold></th>
<th/>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left" colspan="11"><bold>Death</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">No</td>
<td valign="top" align="center">80,908</td>
<td valign="top" align="center">47.7</td>
<td valign="top" align="center">13,676</td>
<td valign="top" align="center">53.5</td>
<td valign="top" align="center">12,900</td>
<td valign="top" align="center">22.3</td>
<td valign="top" align="center">580,377</td>
<td valign="top" align="center">68</td>
<td valign="top" align="center">6,875</td>
<td valign="top" align="center">72.9</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Yes</td>
<td valign="top" align="center">88,751</td>
<td valign="top" align="center">52.3</td>
<td valign="top" align="center">11,888</td>
<td valign="top" align="center">46.5</td>
<td valign="top" align="center">44,958</td>
<td valign="top" align="center">77.7</td>
<td valign="top" align="center">272,658</td>
<td valign="top" align="center">32</td>
<td valign="top" align="center">2,557</td>
<td valign="top" align="center">27.1</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="11"><bold>Sex</bold></td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Men</td>
<td valign="top" align="center">84,947</td>
<td valign="top" align="center">50.1</td>
<td valign="top" align="center">10,331</td>
<td valign="top" align="center">40.4</td>
<td valign="top" align="center">20,533</td>
<td valign="top" align="center">35.5</td>
<td valign="top" align="center">389,526</td>
<td valign="top" align="center">45.7</td>
<td valign="top" align="center">3,167</td>
<td valign="top" align="center">33.6</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Women</td>
<td valign="top" align="center">84,713</td>
<td valign="top" align="center">49.9</td>
<td valign="top" align="center">15,233</td>
<td valign="top" align="center">59.6</td>
<td valign="top" align="center">37,326</td>
<td valign="top" align="center">64.5</td>
<td valign="top" align="center">463,515</td>
<td valign="top" align="center">54.3</td>
<td valign="top" align="center">6,265</td>
<td valign="top" align="center">66.4</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Age (years)</td>
<td valign="top" align="center">75.8</td>
<td valign="top" align="center">7.0</td>
<td valign="top" align="center">76.2</td>
<td valign="top" align="center">7.2</td>
<td valign="top" align="center">80.7</td>
<td valign="top" align="center">7.3</td>
<td valign="top" align="center">75.1</td>
<td valign="top" align="center">7.0</td>
<td valign="top" align="center">74.1</td>
<td valign="top" align="center">6.6</td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">&#x000A0;65&#x02013;74</td>
<td valign="top" align="center">76,560</td>
<td valign="top" align="center">45.1</td>
<td valign="top" align="center">10,876</td>
<td valign="top" align="center">42.5</td>
<td valign="top" align="center">11,465</td>
<td valign="top" align="center">19.8</td>
<td valign="top" align="center">422,171</td>
<td valign="top" align="center">49.5</td>
<td valign="top" align="center">5,158</td>
<td valign="top" align="center">54.7</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">&#x000A0;&#x02265;75</td>
<td valign="top" align="center">93,100</td>
<td valign="top" align="center">54.9</td>
<td valign="top" align="center">14,688</td>
<td valign="top" align="center">57.5</td>
<td valign="top" align="center">46,394</td>
<td valign="top" align="center">80.2</td>
<td valign="top" align="center">430,870</td>
<td valign="top" align="center">50.5</td>
<td valign="top" align="center">4,274</td>
<td valign="top" align="center">45.3</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="11"><bold>Income</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">1st (highest)</td>
<td valign="top" align="center">61,460</td>
<td valign="top" align="center">36.2</td>
<td valign="top" align="center">8,627</td>
<td valign="top" align="center">33.7</td>
<td valign="top" align="center">19,709</td>
<td valign="top" align="center">34.1</td>
<td valign="top" align="center">306,505</td>
<td valign="top" align="center">35.9</td>
<td valign="top" align="center">3,421</td>
<td valign="top" align="center">36.3</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">2nd</td>
<td valign="top" align="center">32,616</td>
<td valign="top" align="center">19.2</td>
<td valign="top" align="center">4,665</td>
<td valign="top" align="center">18.2</td>
<td valign="top" align="center">9,194</td>
<td valign="top" align="center">15.9</td>
<td valign="top" align="center">167,300</td>
<td valign="top" align="center">19.6</td>
<td valign="top" align="center">1,931</td>
<td valign="top" align="center">20.5</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">3rd</td>
<td valign="top" align="center">21,022</td>
<td valign="top" align="center">12.4</td>
<td valign="top" align="center">3,099</td>
<td valign="top" align="center">12.1</td>
<td valign="top" align="center">6,565</td>
<td valign="top" align="center">11.3</td>
<td valign="top" align="center">107,423</td>
<td valign="top" align="center">12.6</td>
<td valign="top" align="center">1,320</td>
<td valign="top" align="center">14</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">4th</td>
<td valign="top" align="center">16,285</td>
<td valign="top" align="center">9.6</td>
<td valign="top" align="center">2,368</td>
<td valign="top" align="center">9.3</td>
<td valign="top" align="center">5,170</td>
<td valign="top" align="center">8.9</td>
<td valign="top" align="center">83,014</td>
<td valign="top" align="center">9.7</td>
<td valign="top" align="center">1,015</td>
<td valign="top" align="center">10.8</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">5th (lowest)</td>
<td valign="top" align="center">38,277</td>
<td valign="top" align="center">22.6</td>
<td valign="top" align="center">6,805</td>
<td valign="top" align="center">26.6</td>
<td valign="top" align="center">17,221</td>
<td valign="top" align="center">29.8</td>
<td valign="top" align="center">188,799</td>
<td valign="top" align="center">22.1</td>
<td valign="top" align="center">1,745</td>
<td valign="top" align="center">18.5</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="11"><bold>Region</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">Seoul metropolitan area</td>
<td valign="top" align="center">72,073</td>
<td valign="top" align="center">42.5</td>
<td valign="top" align="center">7,423</td>
<td valign="top" align="center">29</td>
<td valign="top" align="center">20,509</td>
<td valign="top" align="center">35.4</td>
<td valign="top" align="center">355,576</td>
<td valign="top" align="center">41.7</td>
<td valign="top" align="center">3,563</td>
<td valign="top" align="center">37.8</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Metropolitan cities</td>
<td valign="top" align="center">27,991</td>
<td valign="top" align="center">16.5</td>
<td valign="top" align="center">5,043</td>
<td valign="top" align="center">19.7</td>
<td valign="top" align="center">13,110</td>
<td valign="top" align="center">22.7</td>
<td valign="top" align="center">156,288</td>
<td valign="top" align="center">18.3</td>
<td valign="top" align="center">1,531</td>
<td valign="top" align="center">16.2</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Other areas</td>
<td valign="top" align="center">69,596</td>
<td valign="top" align="center">41</td>
<td valign="top" align="center">13,098</td>
<td valign="top" align="center">51.2</td>
<td valign="top" align="center">24,240</td>
<td valign="top" align="center">41.9</td>
<td valign="top" align="center">341,177</td>
<td valign="top" align="center">40</td>
<td valign="top" align="center">4,338</td>
<td valign="top" align="center">46</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="11"><bold>Disability</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">No</td>
<td valign="top" align="center">128,554</td>
<td valign="top" align="center">75.8</td>
<td valign="top" align="center">18,225</td>
<td valign="top" align="center">71.3</td>
<td valign="top" align="center">39,010</td>
<td valign="top" align="center">67.4</td>
<td valign="top" align="center">671,419</td>
<td valign="top" align="center">78.7</td>
<td valign="top" align="center">7,471</td>
<td valign="top" align="center">79.2</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Yes</td>
<td valign="top" align="center">41,106</td>
<td valign="top" align="center">24.2</td>
<td valign="top" align="center">7,339</td>
<td valign="top" align="center">28.7</td>
<td valign="top" align="center">18,849</td>
<td valign="top" align="center"><bold>32.6</bold></td>
<td valign="top" align="center">181,622</td>
<td valign="top" align="center">21.3</td>
<td valign="top" align="center">1,961</td>
<td valign="top" align="center">20.8</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Charlson comorbidity index</td>
<td valign="top" align="center">5.5</td>
<td valign="top" align="center">3.3</td>
<td valign="top" align="center">5.1</td>
<td valign="top" align="center">3.1</td>
<td valign="top" align="center">5.2</td>
<td valign="top" align="center">2.8</td>
<td valign="top" align="center">4.0</td>
<td valign="top" align="center">2.6</td>
<td valign="top" align="center">4.1</td>
<td valign="top" align="center">2.7</td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">&#x000A0;0</td>
<td valign="top" align="center">5,345</td>
<td valign="top" align="center">3.2</td>
<td valign="top" align="center">946</td>
<td valign="top" align="center">3.7</td>
<td valign="top" align="center">763</td>
<td valign="top" align="center">1.3</td>
<td valign="top" align="center">62,406</td>
<td valign="top" align="center">7.3</td>
<td valign="top" align="center">662</td>
<td valign="top" align="center">7</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">&#x000A0;1&#x02013;2</td>
<td valign="top" align="center">30,793</td>
<td valign="top" align="center">18.1</td>
<td valign="top" align="center">5,182</td>
<td valign="top" align="center">20.3</td>
<td valign="top" align="center">9,931</td>
<td valign="top" align="center">17.2</td>
<td valign="top" align="center">265,010</td>
<td valign="top" align="center">31.1</td>
<td valign="top" align="center">2,924</td>
<td valign="top" align="center">31</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">&#x000A0;&#x02265;3</td>
<td valign="top" align="center">133,522</td>
<td valign="top" align="center">78.7</td>
<td valign="top" align="center">19,436</td>
<td valign="top" align="center">76</td>
<td valign="top" align="center">47,165</td>
<td valign="top" align="center">81.5</td>
<td valign="top" align="center">525,625</td>
<td valign="top" align="center">61.6</td>
<td valign="top" align="center">5,846</td>
<td valign="top" align="center">62</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="11"><bold>Geriatric syndrome (number)</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">0</td>
<td valign="top" align="center">119,337</td>
<td valign="top" align="center">70.3</td>
<td valign="top" align="center">15,506</td>
<td valign="top" align="center">60.7</td>
<td valign="top" align="center">30,210</td>
<td valign="top" align="center">52.2</td>
<td valign="top" align="center">654,498</td>
<td valign="top" align="center">76.7</td>
<td valign="top" align="center">6,547</td>
<td valign="top" align="center">69.4</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">1</td>
<td valign="top" align="center">41,516</td>
<td valign="top" align="center">24.5</td>
<td valign="top" align="center">7,985</td>
<td valign="top" align="center">31.2</td>
<td valign="top" align="center">20,298</td>
<td valign="top" align="center">35.1</td>
<td valign="top" align="center">173,748</td>
<td valign="top" align="center">20.4</td>
<td valign="top" align="center">2,449</td>
<td valign="top" align="center">26</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">2</td>
<td valign="top" align="center">7,788</td>
<td valign="top" align="center">4.6</td>
<td valign="top" align="center">1,820</td>
<td valign="top" align="center">7.1</td>
<td valign="top" align="center">6,397</td>
<td valign="top" align="center">11.1</td>
<td valign="top" align="center">22,578</td>
<td valign="top" align="center">2.6</td>
<td valign="top" align="center">398</td>
<td valign="top" align="center">4.2</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">&#x02265;3</td>
<td valign="top" align="center">1,018</td>
<td valign="top" align="center">0.6</td>
<td valign="top" align="center">253</td>
<td valign="top" align="center">1</td>
<td valign="top" align="center">953</td>
<td valign="top" align="center">1.6</td>
<td valign="top" align="center">2,211</td>
<td valign="top" align="center">0.3</td>
<td valign="top" align="center">38</td>
<td valign="top" align="center">0.4</td>
<td/>
</tr>
<tr>
<td valign="top" align="left" colspan="11"><bold>mFI</bold></td>
<td valign="top" align="center">&#x0003C;0.001</td>
</tr>
<tr>
<td valign="top" align="left">Fit</td>
<td valign="top" align="center">16,278</td>
<td valign="top" align="center">9.6</td>
<td valign="top" align="center">1,686</td>
<td valign="top" align="center">6.6</td>
<td valign="top" align="center">4,826</td>
<td valign="top" align="center">8.3</td>
<td valign="top" align="center">119,416</td>
<td valign="top" align="center">14</td>
<td valign="top" align="center">915</td>
<td valign="top" align="center">9.7</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Mild frail</td>
<td valign="top" align="center">47,440</td>
<td valign="top" align="center">28</td>
<td valign="top" align="center">6,505</td>
<td valign="top" align="center">25.4</td>
<td valign="top" align="center">19,588</td>
<td valign="top" align="center">33.9</td>
<td valign="top" align="center">285,703</td>
<td valign="top" align="center">33.5</td>
<td valign="top" align="center">2,729</td>
<td valign="top" align="center">28.9</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Moderate frail</td>
<td valign="top" align="center">51,330</td>
<td valign="top" align="center">30.3</td>
<td valign="top" align="center">7,997</td>
<td valign="top" align="center">31.3</td>
<td valign="top" align="center">19,825</td>
<td valign="top" align="center">34.3</td>
<td valign="top" align="center">249,467</td>
<td valign="top" align="center">29.2</td>
<td valign="top" align="center">2,834</td>
<td valign="top" align="center">30</td>
<td/>
</tr>
<tr>
<td valign="top" align="left">Severe frail</td>
<td valign="top" align="center">54,612</td>
<td valign="top" align="center">32.2</td>
<td valign="top" align="center">9,376</td>
<td valign="top" align="center">36.7</td>
<td valign="top" align="center">13,620</td>
<td valign="top" align="center">23.5</td>
<td valign="top" align="center">198,455</td>
<td valign="top" align="center">23.3</td>
<td valign="top" align="center">2,954</td>
<td valign="top" align="center">31.3</td>
<td/>
</tr></tbody>
</table>
<table-wrap-foot>
<p>Bold value indicates the highest percentage within the Disability category across discharge destinations.</p>
</table-wrap-foot>
</table-wrap></sec>
<sec>
<label>3.3</label>
<title>Effects of the destination of discharge on mortality</title>
<p>The risk of mortality was significantly higher among those discharged to tertiary/general hospitals (HR: 2.071; 95% CI: 2.055&#x02013;2.087) and LTCHs (HR: 4.274; 95% CI: 4.231&#x02013;4.317) compared to patients discharged home. After adjusting for age, sex, income, region, and disability status, the adjusted hazard ratios (aHRs) for mortality remained elevated for those discharged to tertiary/general hospitals (aHR: 1.977; 95% CI: 1.962&#x02013;1.992), hospitals (aHR: 1.65; 95% CI: 1.619&#x02013;1.68), and LTCHs (aHR: 3.492; 95% CI: 3.457&#x02013;3.528). After comorbidities, geriatric syndromes, and frailty were adjusted, the aHR for mortality among patients discharged to LTCHs remained significantly higher (aHR: 2.922; 95% CI: 2.892&#x02013;2.952) compared to those discharged home (<xref ref-type="table" rid="T3">Table 3</xref>).</p>
<table-wrap position="float" id="T3">
<label>Table 3</label>
<caption><p>Cox regression analysis of factors related to morality.</p></caption>
<table frame="box" rules="all">
<thead>
<tr>
<th valign="top" align="left"><bold>Variables</bold></th>
<th valign="top" align="center"><bold>crude HR</bold></th>
<th valign="top" align="center" colspan="3">aHR</th>
</tr>
<tr>
<th/>
<th valign="top" align="center"><bold>Model 1</bold></th>
<th valign="top" align="center"><bold>Model 2</bold></th>
<th valign="top" align="center"><bold>Model 3</bold></th>
<th valign="top" align="center"><bold>Model 4</bold></th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left" colspan="5"><bold>Discharge destination</bold></td>
</tr>
<tr>
<td valign="top" align="left">Tertiary and General Hospitals</td>
<td valign="top" align="center">2.071 (2.055&#x02013;2.087)</td>
<td valign="top" align="center">1.977 (1.962&#x02013;1.992)</td>
<td/>
<td valign="top" align="center">1.806 (1.793&#x02013;1.82)</td>
</tr>
<tr>
<td valign="top" align="left">Hospital</td>
<td valign="top" align="center">1.698 (1.667&#x02013;1.729)</td>
<td valign="top" align="center">1.65 (1.619&#x02013;1.68)</td>
<td/>
<td valign="top" align="center">1.48 (1.453&#x02013;1.507)</td>
</tr>
<tr>
<td valign="top" align="left">Long-term Care Hospital</td>
<td valign="top" align="center">4.274 (4.231&#x02013;4.317)</td>
<td valign="top" align="center">3.492 (3.457&#x02013;3.528)</td>
<td/>
<td valign="top" align="center">2.922 (2.892&#x02013;2.952)</td>
</tr>
<tr>
<td valign="top" align="left">Home</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td/>
<td valign="top" align="center">REF</td>
</tr>
<tr>
<td valign="top" align="left">Others</td>
<td valign="top" align="center">0.836 (0.804&#x02013;0.87)</td>
<td valign="top" align="center">0.937 (0.901&#x02013;0.974)</td>
<td/>
<td valign="top" align="center">0.922 (0.887&#x02013;0.959)</td>
</tr>
<tr>
<td valign="top" align="left" colspan="5"><bold>Charlson comorbidity index</bold></td>
</tr>
<tr>
<td valign="top" align="left">0</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
</tr>
<tr>
<td valign="top" align="left">1&#x02013;2</td>
<td valign="top" align="center">1.776 (1.739&#x02013;1.813)</td>
<td valign="top" align="center">1.612 (1.579&#x02013;1.646)</td>
<td valign="top" align="center">1.561 (1.529&#x02013;1.593)</td>
<td valign="top" align="center">1.63 (1.596&#x02013;1.665)</td>
</tr>
<tr>
<td valign="top" align="left">&#x02265;3</td>
<td valign="top" align="center">4 (3.922&#x02013;4.08)</td>
<td valign="top" align="center">3.246 (3.182&#x02013;3.311)</td>
<td valign="top" align="center">2.912 (2.855&#x02013;2.971)</td>
<td valign="top" align="center">3.116 (3.054&#x02013;3.18)</td>
</tr>
<tr>
<td valign="top" align="left" colspan="5"><bold>Geriatric syndrome (number)</bold></td>
</tr>
<tr>
<td valign="top" align="left">0</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
</tr>
<tr>
<td valign="top" align="left">1</td>
<td valign="top" align="center">1.515 (1.505&#x02013;1.526)</td>
<td valign="top" align="center">1.41 (1.401&#x02013;1.42)</td>
<td valign="top" align="center">1.314 (1.305&#x02013;1.323)</td>
<td valign="top" align="center">1.299 (1.29&#x02013;1.309)</td>
</tr>
<tr>
<td valign="top" align="left">2</td>
<td valign="top" align="center">2.649 (2.615&#x02013;2.683)</td>
<td valign="top" align="center">2.263 (2.234&#x02013;2.293)</td>
<td valign="top" align="center">1.867 (1.843&#x02013;1.892)</td>
<td valign="top" align="center">1.833 (1.809&#x02013;1.857)</td>
</tr>
<tr>
<td valign="top" align="left">&#x02265;3</td>
<td valign="top" align="center">3.724 (3.602&#x02013;3.85)</td>
<td valign="top" align="center">2.96 (2.863&#x02013;3.061)</td>
<td valign="top" align="center">2.236 (2.163&#x02013;2.312)</td>
<td valign="top" align="center">2.189 (2.117&#x02013;2.263)</td>
</tr>
<tr>
<td valign="top" align="left" colspan="5"><bold>mFI</bold></td>
</tr>
<tr>
<td valign="top" align="left">Fit</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
</tr>
<tr>
<td valign="top" align="left">Mild frail</td>
<td valign="top" align="center">1.159 (1.147&#x02013;1.172)</td>
<td valign="top" align="center">1.03 (1.019&#x02013;1.042)</td>
<td valign="top" align="center">0.987 (0.976&#x02013;0.998)</td>
<td valign="top" align="center">0.851 (0.842&#x02013;0.861)</td>
</tr>
<tr>
<td valign="top" align="left">Moderate frail</td>
<td valign="top" align="center">1.364 (1.349&#x02013;1.379)</td>
<td valign="top" align="center">1.094 (1.082&#x02013;1.106)</td>
<td valign="top" align="center">1.024 (1.013&#x02013;1.035)</td>
<td valign="top" align="center">0.791 (0.782&#x02013;0.8)</td>
</tr>
<tr>
<td valign="top" align="left">Severe frail</td>
<td valign="top" align="center">1.648 (1.63&#x02013;1.667)</td>
<td valign="top" align="center">1.185 (1.172&#x02013;1.199)</td>
<td valign="top" align="center">1.093 (1.081&#x02013;1.105)</td>
<td valign="top" align="center">0.757 (0.749&#x02013;0.766)</td>
</tr></tbody>
</table>
<table-wrap-foot>
<p>Model 1: unadjusted.</p>
<p>Model 2: adjusted for age, sex, income, region, disability.</p>
<p>Model 3: model 2 &#x0002B; discharge destination.</p>
<p>Model 4: model 3 &#x0002B; CCI, GS, mFI.</p>
<p>HR, hazard ratio; aHR, adjusted hazard ratio.</p>
</table-wrap-foot>
</table-wrap>
<p>Mortality risk increased progressively with higher CCI scores, a greater number of geriatric syndromes, and more severe levels of frailty. These trends persisted even after adjusting for age, sex, income, region, disability status, and discharge destination. The aHR were 2.912 (95% CI: 2.855&#x02013;2.971) for patients with a CCI score &#x02265;3, 2.236 (95% CI: 2.163&#x02013;2.312) for those with three or more geriatric syndromes, and 1.093 (95% CI: 1.081&#x02013;1.105) for patients with severe frailty (<xref ref-type="table" rid="T3">Table 3</xref>). When CCI, geriatric syndromes, and the multimorbidity frailty index (mFI) were included simultaneously in the fully adjusted model (Model 4), the hazard ratios associated with frailty were attenuated and, in some categories, reversed in direction. This pattern likely reflects statistical overadjustment arising from substantial conceptual and empirical overlap among these vulnerability indicators. Because the mFI is constructed as a deficit accumulation index incorporating multimorbidity and functional impairments, adjustment for both CCI and geriatric syndromes may partition shared variance across correlated constructs, thereby altering the apparent independent association of frailty with mortality. The impact of comorbidities, geriatric syndromes, and frailty on mortality risk according to discharge destination varied when considered individually and in combination, even after adjusting for multiple confounding variables (<xref ref-type="supplementary-material" rid="SM1">Supplementary Table 2</xref>).</p></sec>
<sec>
<label>3.4</label>
<title>Impact of geriatric health state on mortality according to discharge destination</title>
<p>CCI was consistently associated with increased mortality risk across all discharge destinations, with the greatest risk observed among individuals with CCI scores of &#x02265;3. This trend persisted even in Model 2, which was adjusted for age, sex, income, region, and disability. Specifically, the aHR for mortality among those with CCI &#x02265; 3 was 4.146 (95% CI: 3.886&#x02013;4.423) for patients discharged to tertiary/general hospitals, 3.041 (95% CI: 2.616&#x02013;3.535) for those discharged to hospitals, 2.341 (95% CI: 2.104&#x02013;2.605) for those discharged to LTCHs, and 2.752 (95% CI: 2.693&#x02013;2.812) for those discharged to home.</p>
<p>Similarly, the risk of mortality increased progressively with the number of geriatric syndromes, regardless of the discharge destination. Among patients with three or more geriatric syndromes, the highest risk was observed in those who were discharged home (aHR, 3.186; 95% CI: 3.035&#x02013;3.344). The association of frailty with mortality risk varied according to the discharge destination. Among patients discharged, those in the most severe frailty group had a significantly increased risk of mortality (aHR, 1.261; 95% CI, 1.244&#x02013;1.279) (<xref ref-type="table" rid="T4">Table 4</xref>).</p>
<table-wrap position="float" id="T4">
<label>Table 4</label>
<caption><p>Cox regression analysis of factors related to morality.</p></caption>
<table frame="box" rules="all">
<thead>
<tr>
<th valign="top" align="left"><bold>Variables</bold></th>
<th valign="top" align="center" colspan="6">Discharge destination, HR (95% CI)</th>
</tr>
<tr>
<th/>
<th/>
<th valign="top" align="center"><bold>Tertiary and general hospitals</bold></th>
<th valign="top" align="center"><bold>Hospital</bold></th>
<th valign="top" align="center"><bold>Long-term Care Hospital</bold></th>
<th valign="top" align="center"><bold>Home</bold></th>
<th valign="top" align="center"><bold>Others</bold></th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left" rowspan="14">Model 1</td>
<td valign="top" align="left" colspan="6"><bold>Charlson comorbidity index</bold></td>
</tr>
 <tr>
<td valign="top" align="center">0</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
</tr>
 <tr>
<td valign="top" align="center">1-2</td>
<td valign="top" align="center">1.965 (1.837&#x02013;2.102)</td>
<td valign="top" align="center">1.631 (1.393&#x02013;1.91)</td>
<td valign="top" align="center">1.989 (1.784&#x02013;2.217)</td>
<td valign="top" align="center">1.645 (1.608&#x02013;1.683)</td>
<td valign="top" align="center">1.494 (1.162&#x02013;1.922)</td>
</tr>
 <tr>
<td valign="top" align="center">&#x02265;3</td>
<td valign="top" align="center">4.673 (4.38&#x02013;4.985)</td>
<td valign="top" align="center">3.808 (3.277&#x02013;4.425)</td>
<td valign="top" align="center">2.681 (2.41&#x02013;2.983)</td>
<td valign="top" align="center">3.416 (3.343&#x02013;3.49)</td>
<td valign="top" align="center">3.891 (3.067&#x02013;4.938)</td>
</tr>
 <tr>
<td valign="top" align="left" colspan="6"><bold>Geriatric syndrome (number)</bold></td>
</tr>
 <tr>
<td valign="top" align="center">0</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
</tr>
 <tr>
<td valign="top" align="center">1</td>
<td valign="top" align="center">1.273 (1.254&#x02013;1.293)</td>
<td valign="top" align="center">1.301 (1.251&#x02013;1.353)</td>
<td valign="top" align="center">1.092 (1.07&#x02013;1.114)</td>
<td valign="top" align="center">1.481 (1.468&#x02013;1.494)</td>
<td valign="top" align="center">1.366 (1.253&#x02013;1.488)</td>
</tr>
 <tr>
<td valign="top" align="center">2</td>
<td valign="top" align="center">1.814 (1.765&#x02013;1.865)</td>
<td valign="top" align="center">1.962 (1.845&#x02013;2.087)</td>
<td valign="top" align="center">1.24 (1.204&#x02013;1.278)</td>
<td valign="top" align="center">2.666 (2.619&#x02013;2.713)</td>
<td valign="top" align="center">2.102 (1.798&#x02013;2.457)</td>
</tr>
 <tr>
<td valign="top" align="center">&#x02265;3</td>
<td valign="top" align="center">2.153 (2.009&#x02013;2.308)</td>
<td valign="top" align="center">2.74 (2.377&#x02013;3.157)</td>
<td valign="top" align="center">1.31 (1.222&#x02013;1.405)</td>
<td valign="top" align="center">4.125 (3.93&#x02013;4.33)</td>
<td valign="top" align="center">4.694 (3.208&#x02013;6.869)</td>
</tr>
 <tr>
<td valign="top" align="left" colspan="6"><bold>Frailty (mFI)</bold></td>
</tr>
 <tr>
<td valign="top" align="center">Fit</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
</tr>
 <tr>
<td valign="top" align="center">Mild frail</td>
<td valign="top" align="center">0.915 (0.892&#x02013;0.938)</td>
<td valign="top" align="center">1.046 (0.961&#x02013;1.137)</td>
<td valign="top" align="center">0.941 (0.908&#x02013;0.976)</td>
<td valign="top" align="center">1.152 (1.137&#x02013;1.168)</td>
<td valign="top" align="center">0.987 (0.844&#x02013;1.154)</td>
</tr>
 <tr>
<td valign="top" align="center">Moderate frail</td>
<td valign="top" align="center">0.908 (0.886&#x02013;0.931)</td>
<td valign="top" align="center">1.086 (1&#x02013;1.179)</td>
<td valign="top" align="center">0.921 (0.889&#x02013;0.954)</td>
<td valign="top" align="center">1.403 (1.384&#x02013;1.422)</td>
<td valign="top" align="center">1.055 (0.904&#x02013;1.231)</td>
</tr>
 <tr>
<td valign="top" align="center">Severe frail</td>
<td valign="top" align="center">0.957 (0.935&#x02013;0.981)</td>
<td valign="top" align="center">1.28 (1.181&#x02013;1.387)</td>
<td valign="top" align="center">0.884 (0.851&#x02013;0.917)</td>
<td valign="top" align="center">1.791 (1.767&#x02013;1.815)</td>
<td valign="top" align="center">1.514 (1.304&#x02013;1.757)</td>
</tr>
<tr>
<td valign="top" align="left" rowspan="14">Model 2</td>
<td valign="top" align="left" colspan="6"><bold>Charlson comorbidity index</bold></td>
</tr>
 <tr>
<td valign="top" align="center">0</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
</tr>
 <tr>
<td valign="top" align="center">1-2</td>
<td valign="top" align="center">1.858 (1.737&#x02013;1.987)</td>
<td valign="top" align="center">1.462 (1.248&#x02013;1.711)</td>
<td valign="top" align="center">1.803 (1.618&#x02013;2.011)</td>
<td valign="top" align="center">1.49 (1.457&#x02013;1.525)</td>
<td valign="top" align="center">1.382 (1.074&#x02013;1.778)</td>
</tr>
 <tr>
<td valign="top" align="center">&#x02265;3</td>
<td valign="top" align="center">4.146 (3.886&#x02013;4.423)</td>
<td valign="top" align="center">3.041 (2.616&#x02013;3.535)</td>
<td valign="top" align="center">2.341 (2.104&#x02013;2.605)</td>
<td valign="top" align="center">2.752 (2.693&#x02013;2.812)</td>
<td valign="top" align="center">3.154 (2.484&#x02013;4.005)</td>
</tr>
 <tr>
<td valign="top" align="left" colspan="6"><bold>Geriatric syndrome (number)</bold></td>
</tr>
 <tr>
<td valign="top" align="center">0</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
</tr>
 <tr>
<td valign="top" align="center">1</td>
<td valign="top" align="center">1.241 (1.222&#x02013;1.26)</td>
<td valign="top" align="center">1.256 (1.207&#x02013;1.307)</td>
<td valign="top" align="center">1.105 (1.083&#x02013;1.128)</td>
<td valign="top" align="center">1.374 (1.362&#x02013;1.386)</td>
<td valign="top" align="center">1.352 (1.239&#x02013;1.475)</td>
</tr>
 <tr>
<td valign="top" align="center">2</td>
<td valign="top" align="center">1.706 (1.659&#x02013;1.754)</td>
<td valign="top" align="center">1.792 (1.683&#x02013;1.908)</td>
<td valign="top" align="center">1.256 (1.219&#x02013;1.294)</td>
<td valign="top" align="center">2.26 (2.22&#x02013;2.301)</td>
<td valign="top" align="center">1.947 (1.663&#x02013;2.28)</td>
</tr>
 <tr>
<td valign="top" align="center">&#x02265;3</td>
<td valign="top" align="center">1.999 (1.865&#x02013;2.143)</td>
<td valign="top" align="center">2.371 (2.056&#x02013;2.735)</td>
<td valign="top" align="center">1.296 (1.208&#x02013;1.389)</td>
<td valign="top" align="center">3.186 (3.035&#x02013;3.344)</td>
<td valign="top" align="center">3.188 (2.175&#x02013;4.674)</td>
</tr>
 <tr>
<td valign="top" align="left" colspan="6"><bold>Frailty (mFI)</bold></td>
</tr>
 <tr>
<td valign="top" align="center">Fit</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
<td valign="top" align="center">REF</td>
</tr>
 <tr>
<td valign="top" align="center">Mild frail</td>
<td valign="top" align="center">0.849 (0.829&#x02013;0.871)</td>
<td valign="top" align="center">0.977 (0.898&#x02013;1.063)</td>
<td valign="top" align="center">0.901 (0.869&#x02013;0.934)</td>
<td valign="top" align="center">1.019 (1.006&#x02013;1.033)</td>
<td valign="top" align="center">0.928 (0.793&#x02013;1.085)</td>
</tr>
 <tr>
<td valign="top" align="center">Moderate frail</td>
<td valign="top" align="center">0.79 (0.771&#x02013;0.81)</td>
<td valign="top" align="center">0.924 (0.85&#x02013;1.003)</td>
<td valign="top" align="center">0.853 (0.823&#x02013;0.884)</td>
<td valign="top" align="center">1.111 (1.096&#x02013;1.126)</td>
<td valign="top" align="center">0.884 (0.756&#x02013;1.033)</td>
</tr>
 <tr>
<td valign="top" align="center">Severe frail</td>
<td valign="top" align="center">0.768 (0.75&#x02013;0.787)</td>
<td valign="top" align="center">0.976 (0.9&#x02013;1.059)</td>
<td valign="top" align="center">0.794 (0.765&#x02013;0.824)</td>
<td valign="top" align="center">1.261 (1.244&#x02013;1.279)</td>
<td valign="top" align="center">1.079 (0.927&#x02013;1.256)</td>
</tr></tbody>
</table>
<table-wrap-foot>
<p>Model 1: unadjusted .</p>
<p>Model 2: adjusted for age, sex, income, region, disability.</p>
<p>HR, hazard ratio; CI, confidence interval.</p>
</table-wrap-foot>
</table-wrap></sec>
<sec>
<label>3.5</label>
<title>Utilization of emergency, outpatient (OPD), and inpatient services varies according to health status indicators and type of healthcare institution</title>
<p>The utilization of emergency, OPD, and inpatient services varies across different types of healthcare institutions, including general hospitals, long-term care hospitals, home care, and other facilities. OPD services at general hospitals were the most frequently utilized, with a mean of 40.3 outpatient visits per participant (SD = 37.5) during the follow-up period. Among patients with a CCI score of 0, OPD service usage at general hospitals averaged 26.9 visits (SD = 23.9), which was lower than those with a CCI score &#x02265; 3, who averaged 43.9 visits (SD = 40.7). A higher CCI score (&#x02265;3) was associated with increased utilization of inpatient services in long-term care hospitals, averaging 97.5 visits (SD = 121.6). For patients without geriatric syndromes, OPD service usage at general hospitals averaged 40.1 visits (SD = 36.4). However, this decreased to an average of 28.6 visits (SD = 35.2) for patients with three or more geriatric syndromes. Conversely, inpatient service utilization in long-term care hospitals increased significantly with the number of geriatric syndromes, reaching an average of 160.5 visits (SD = 130.0) for those with three or more syndromes. Similarly, patients with low mFI scores demonstrated an average of 23.1 OPD visits (SD = 20.7) at general hospitals, whereas those in the highest quartile (4Q) of mFI scores exhibited a marked increase, averaging 59.8 visits (SD = 48.1). Inpatient service utilization in long-term care hospitals was highest among patients in the 4Q mFI group, with an average of 90.3 visits (SD = 112.6). These findings highlight the influence of comorbidities, frailty, and geriatric syndromes on healthcare service utilization patterns across healthcare settings (<xref ref-type="supplementary-material" rid="SM1">Supplementary Table 3</xref>).</p></sec></sec>
<sec sec-type="discussion" id="s4">
<label>4</label>
<title>Discussion</title>
<sec>
<label>4.1</label>
<title>Key findings</title>
<p>This nationwide, population-based cohort study analyzed over 1 million older adults discharged from acute care hospitals in South Korea, providing robust evidence of the relationships among discharge destination, comorbidities, geriatric syndromes, frailty, and mortality risk.</p>
<p>Discharge destination was a significant predictor of mortality. Patients discharged to LTCHs exhibited an aHR of 2.922 (95% CI: 2.892&#x02013;2.952) compared to those discharged home, indicating nearly a threefold higher risk of mortality. Additionally, the presence of multiple comorbidities (CCI &#x02265; 3; aHR 2.912, 95% CI: 2.855&#x02013;2.971), geriatric syndromes (&#x02265;3; aHR 2.236, 95% CI: 2.163&#x02013;2.312), and severe frailty (aHR 1.09, 95% CI: 1.081&#x02013;1.105) was independently associated with increased mortality, regardless of discharge setting. Among patients with severe frailty (aHR 1.26, 95% CI 1.244&#x02013;1.279) or multiple geriatric syndromes (aHR 3.186, 95% CI 3.035&#x02013;3.344), those discharged exhibited the highest relative mortality risk (aHR: 1.977; 95% CI: 1.962&#x02013;1.992). This highlights the substantial vulnerability of patients with multiple comorbidities, geriatric syndrome, and frailty.</p>
<p>Among patients classified under &#x0201C;Others&#x0201D; as discharge destinations, those with three or more geriatric syndromes (aHR 3.188; 95% CI: 2.484&#x02013;4.005) and those with severe frailty (a HR 1.079; 95% CI: 0.927&#x02013;1.256) exhibited a higher mortality risk. However, the relatively wide confidence interval suggests some uncertainty regarding the magnitude of this effect. While greater frailty severity was generally associated with higher mortality risk, an unexpected trend was observed after adjusting for multiple confounding factors (adjusted for CCI and geriatric syndrome), the mortality risk appeared to decrease in patients with moderate to severe frailty (severe frailty: aHR 0.757). This finding suggests a complex interplay between frailty and mortality, warranting further investigation into the underlying mechanisms of this relationship.</p>
<p>Furthermore, higher levels of comorbidities and frailty were associated with a substantial increase in inpatient healthcare utilization in LTCHs. This highlights the complex interplay between health status and care environment in shaping outcomes for older adults.</p></sec>
<sec>
<label>4.2</label>
<title>Comparison with existing literature</title>
<p>Our findings align with those of previous studies, confirming that comorbidities, geriatric syndromes, and frailty contribute to increased mortality. Various studies have highlighted the significant impact of comorbidities, geriatric syndromes, and frailty on mortality among older adults. A cohort study involving 18,322 patients with heart failure demonstrated that comorbidities substantially increased mortality risk, with HR ranging from 1.16 1.93 (<xref ref-type="bibr" rid="B30">30</xref>). Similarly, a meta-analysis has revealed that individuals with two or more chronic conditions faced a 1.73-fold higher risk of death, which increased by 2.72-fold for those with three or more conditions (<xref ref-type="bibr" rid="B31">31</xref>). In Mexico, cognitive impairment and dependency have been identified as independent predictors of in-hospital mortality among older adults (<xref ref-type="bibr" rid="B32">32</xref>). Findings from Taiwan showed that the accumulation of geriatric syndromes significantly amplified the mortality risk (<xref ref-type="bibr" rid="B33">33</xref>). Furthermore, the FRADEA cohort study in Spain (<xref ref-type="bibr" rid="B34">34</xref>) and the SHARE study across Europe confirmed a strong association between frailty and all-cause mortality, emphasizing the critical role of disability management in those aged &#x02265;80 years (<xref ref-type="bibr" rid="B35">35</xref>). These findings underscore the importance of addressing comorbidities, geriatric syndromes, and frailty in geriatric care to mitigate mortality risks.</p>
<p>Although existing studies have compared the impacts of comorbidities, geriatric syndromes, and frailty on mortality, they have typically been limited to specific disease groups or conducted on small populations within certain regions. By contrast, this study used big data to analyze a larger sample size, overcoming the limitations of previous small-scale cohort studies and region-specific research.</p>
<p>Previous studies have also reported that the discharge destination of older patients influences both mortality and healthcare utilization (<xref ref-type="bibr" rid="B7">7</xref>, <xref ref-type="bibr" rid="B9">9</xref>, <xref ref-type="bibr" rid="B36">36</xref>). In particular, the finding that transfers to long-term care hospitals or facilities are associated with higher mortality rates than discharges to home is consistent with the results of the present study. Furthermore, it distinguishes itself by comparing the mortality risks based on discharge destinations, such as institutional care settings vs. home discharge, in relation to comorbidities and geriatric syndromes, including frailty. Our study extended these results by incorporating a broader range of discharge destinations and quantifying the additive effects of frailty and geriatric syndromes across these settings.</p>
<p>Importantly, our study revealed that the mortality risk for vulnerable patients (i.e., those with severe frailty or multiple geriatric syndromes) discharged home may be even higher than that for those discharged to institutions, a nuance less emphasized in previous literature.</p>
<p>In contrast to previous research, the attenuation or reversal of the association between frailty and mortality observed in the fully adjusted model represents an important methodological consideration. This finding should not be interpreted as evidence of a protective effect of frailty, but rather as a consequence of overadjustment and collinearity arising from the simultaneous adjustment for the Charlson Comorbidity Index (CCI), geriatric syndromes, and the multimorbidity frailty index (mFI). The mFI is an ICD-10&#x02013;based deficit accumulation index that incorporates multiple diseases and functional impairments, many of which conceptually overlap with CCI and geriatric syndrome variables (<xref ref-type="bibr" rid="B24">24</xref>). When these correlated vulnerability indicators are mutually adjusted, the shared construct of vulnerability may be statistically decomposed, leading to unstable or counterintuitive effect estimates, a phenomenon that has also been reported in prior studies using administrative data&#x02013;based frailty measures (<xref ref-type="bibr" rid="B16">16</xref>). By contrast, in Models 1&#x02013;3, which avoided redundant adjustment for overlapping vulnerability indicators, the association between frailty and mortality remained consistent with established clinical and epidemiological evidence (<xref ref-type="bibr" rid="B14">14</xref>). Accordingly, Model 4 should be interpreted with caution and understood as an exploratory analysis of the relative contributions of vulnerability components rather than as supporting causal inference.</p>
<p>Most previous studies have examined frailty, multimorbidity, geriatric syndromes, or discharge destination as independent predictors of post-discharge mortality, often within disease-specific or regionally limited cohorts (<xref ref-type="bibr" rid="B14">14</xref>, <xref ref-type="bibr" rid="B31">31</xref>, <xref ref-type="bibr" rid="B34">34</xref>). Evidence from North America and Europe consistently shows that frailty and multimorbidity are strong determinants of mortality risk after hospitalization, while other studies have emphasized elevated mortality among patients discharged to institutional care settings such as long-term care or skilled nursing facilities (<xref ref-type="bibr" rid="B6">6</xref>, <xref ref-type="bibr" rid="B16">16</xref>, <xref ref-type="bibr" rid="B35">35</xref>, <xref ref-type="bibr" rid="B37">37</xref>). However, few investigations have simultaneously evaluated these interrelated domains within a unified analytical framework, despite their substantial conceptual and clinical overlap.</p>
<p>By integrating discharge destination, comorbidity burden, geriatric syndromes, and frailty in a single nationwide cohort of more than 1.1 million older adults, the present study extends prior work by demonstrating that post-discharge mortality risk is shaped by the interaction of multidimensional vulnerability factors, rather than by any single domain alone. Importantly, we show that severely frail individuals may face a markedly elevated risk of death even when discharged home, challenging the prevailing assumption that institutional discharge uniformly represents the highest-risk pathway (<xref ref-type="bibr" rid="B9">9</xref>, <xref ref-type="bibr" rid="B36">36</xref>, <xref ref-type="bibr" rid="B38">38</xref>). This finding highlights the limitation of using discharge destination alone as a proxy for patient vulnerability and underscores the need for risk-stratified transitional care strategies that incorporate comprehensive geriatric assessment&#x02014;particularly frailty and geriatric syndromes&#x02014;across care settings, with direct implications for clinical practice and health policy in aging societies (<xref ref-type="bibr" rid="B4">4</xref>, <xref ref-type="bibr" rid="B6">6</xref>).</p></sec>
<sec>
<label>4.3</label>
<title>Possible explanations</title>
<p>Differences in mortality rates according to the discharge destination may be attributed to variations in patients&#x00027; health status, socioeconomic factors, and access to healthcare resources.</p>
<p>Patients transferred to long-term care hospitals were older and had a higher prevalence of comorbidities, disabilities, and geriatric syndromes, which may have contributed to a poorer prognosis. Additionally, among patients with higher geriatric syndrome burden and elevated mFI scores, inpatient services were used more frequently than OPD services. Thus, individuals with greater frailty may be more likely to receive palliative or supportive care rather than active treatment, which may in turn increase mortality risk. By contrast, patients discharged home were generally in better health and more likely to benefit from family and social support.</p>
<p>Our findings enhance our understanding of healthcare utilization patterns in aging societies. Indicators related to frailty were strongly associated with an increased mortality risk among patients discharged home, suggesting that intensive management is particularly necessary for individuals with frailty receiving home-based care. These results have important implications for the development of tailored healthcare policies for older adults.</p>
<p>Among patients with severe frailty, those discharged home exhibited the highest adjusted risk of mortality, suggesting that home discharge does not necessarily ensure adequate post-discharge care for this high-risk group. We postulate that severely frail patients discharged home may experience increased mortality due to insufficient access to structured post-acute care, including regular medical follow-up, rehabilitation services, nursing care, and systematic monitoring (<xref ref-type="bibr" rid="B4">4</xref>, <xref ref-type="bibr" rid="B6">6</xref>). In addition, the burden placed on family caregivers, delayed recognition of clinical deterioration, and fragmentation between acute hospital care and community-based services may further contribute to adverse outcomes (<xref ref-type="bibr" rid="B9">9</xref>, <xref ref-type="bibr" rid="B36">36</xref>). These findings highlight a critical gap in current post-discharge care models and underscore the importance of risk-based discharge planning, strengthened transitional care programs, and integrated home-based medical care for severely frail older adults from both public health and policy perspectives (<xref ref-type="bibr" rid="B4">4</xref>, <xref ref-type="bibr" rid="B38">38</xref>).</p></sec>
<sec>
<label>4.4</label>
<title>Clinical implications</title>
<p>Building on the observation that severely frail patients discharged home face substantially elevated mortality risk, these findings have important clinical and public health implications for post-discharge care delivery in older adults.</p>
<p>Older patients require post-acute healthcare services after hospitalization because of illness or injury (<xref ref-type="bibr" rid="B38">38</xref>). These services play critical roles in promoting recovery, enhancing functional capacity, and managing chronic diseases. Given the complexity and heterogeneity of healthcare needs, a disease-centered approach is insufficient. Therefore, comprehensive and integrated care strategies are required.</p>
<p>Our findings have significant implications for discharge planning and post-acute care management in rapidly aging societies. Discharge planning for older patients should be tailored to comorbidities, geriatric syndromes, frailty status, and intended discharge destination. Tools such as the FI and geriatric syndrome indicators facilitate the early identification of high-risk patients, offering evidence-based guidance for selecting appropriate discharge settings. This data-driven approach provides critical insights for policymakers and healthcare providers by promoting the effective integration of community-based healthcare services and resources.</p>
<p>For older patients discharged home, the increased risk of mortality underscores the importance of robust discharge planning and personalized post-acute care strategies. Comprehensive care programs, including home-nursing visits and rehabilitation services, should be implemented and customized to address individual patient needs. Proactive identification of high-risk patients using frailty and geriatric syndrome indices combined with enhanced home-based medical and social support can mitigate adverse outcomes.</p>
<p>Effective discharge planning and post-acute care for older patients require a personalized approach that incorporates assessments of frailty and geriatric syndromes. By tailoring care plans to each patient&#x00027;s specific health status, health outcomes could be optimized, and patient-centered continuity of care could be supported. In addition, leveraging integrated community-based healthcare resources could promote the sustainable and efficient management of healthcare needs in this population. Such individualized strategies may also reduce unnecessary hospitalizations and overuse of healthcare resources, ultimately improving the quality and continuity of care for older adults. Policymakers and clinicians should prioritize the integration of structured follow-up and community-based resources for vulnerable older adults, regardless of their discharge destination, to enhance their survival rates and improve their quality of life.</p></sec>
<sec>
<label>4.5</label>
<title>Limitations and strengths</title>
<p>This study had some limitations. First, this study utilized claims data from the National Health Insurance Service (NHIS), which lacks critical clinical information such as disease severity, functional status changes, and cognitive function. Consequently, the potential for classification errors and unmeasured confounding variables remains. Although the modified frailty index (mFI) employed in this research has been validated in prior studies, it fails to fully capture the multidimensional functional frailty states identified through comprehensive geriatric assessments. Moreover, the administrative-data-based definitions of geriatric syndromes exclude multifactorial conditions like cognitive impairment, functional decline, sensory deficits, and malnutrition, potentially underestimating the actual prevalence and clinical significance of frailty and geriatric syndromes.</p>
<p>Second, the operational definition of frailty and geriatric syndromes in this study relies on a simplistic summative approach, omitting key elements such as severity, duration, and interactions. This limitation poses challenges to the interpretability of the findings. As an observational study, it inherently cannot establish causal relationships. While adjustments were made for various confounders to analyze mortality risks by discharge destination, the possibility that discharge destinations reflect patients&#x00027; baseline conditions cannot be entirely excluded. Additionally, critical factors such as social support, patient preferences, and regional healthcare policies, which are essential for understanding the relationship between discharge destinations and patient outcomes, were absent from the dataset.</p>
<p>Third, as the study is based on Korean NHIS data, its findings are contextually limited to the Korean healthcare system. The unique structural characteristics of Korea&#x00027;s healthcare system may hinder the direct applicability of the results to other countries. For instance, while Korean long-term care hospitals share similarities with skilled nursing facilities (SNFs) in the United States or Kaigo Iryo-in in Japan, institutional differences exist. Such discrepancies necessitate caution when generalizing the findings to other healthcare environments.</p>
<p>Fourth, the classification of discharge destinations in this study reflects national characteristics, potentially introducing temporal variations and selection bias. Furthermore, the classification system lacked granularity, failing to differentiate between critical categories such as skilled nursing facilities, assisted living facilities, and rehabilitation hospitals. This limitation may restrict the interpretability and generalizability of the results.</p>
<p>Fifth, the absence of <italic>post-hoc</italic> analyses precluded a more detailed exploration of outcomes in specific subgroups or the evaluation of the impact of potential confounders. Additionally, despite excluding 16,562 cases due to missing data, the study did not provide a detailed explanation of this exclusion nor conduct sensitivity analyses to assess its impact on the results. These omissions represent significant limitations, potentially undermining the reliability and generalizability of the findings.</p>
<p>Nevertheless, the strengths of this study include its large, nationally representative sample; comprehensive assessment of comorbidities, geriatric syndromes, and frailty; and robust follow-up for mortality using the national registry. The use of validated indices and stratified analysis by discharge destination provided nuanced insights into risk stratification.</p></sec>
<sec>
<label>4.6</label>
<title>Future directions</title>
<p>Future research should prioritize the standardization of quantitative assessment tools for frailty and geriatric syndromes to enhance the reliability and reproducibility of analyses. This approach will enable large-scale studies that include diverse populations, thereby increasing the generalizability of findings. Additionally, to elucidate the relationships between discharge destinations, geriatric health conditions, and mortality, prospective studies integrating detailed clinical and functional data, as well as the perspectives of patients and caregivers, are essential. Such studies can leverage advanced methodologies, including clustering techniques and machine learning approaches, to provide a deeper understanding of the complex interactions between these factors. Particular emphasis should be placed on conducting interventional studies aimed at evaluating the effectiveness of personalized transitional care programs for frail older adults. These programs are expected to play a significant role in improving post-discharge health outcomes, reducing hospital readmissions, and lowering mortality rates among this vulnerable population. Furthermore, research should focus on identifying the impact of modifiable factors, such as healthcare quality, resource availability, staffing patterns, and discharge environments, on mortality. Investigating these factors will provide critical insights for developing refined strategies to reduce mortality and improve health outcomes in the growing older population. Such comprehensive and multi-faceted research efforts will contribute to advancing clinical practices and healthcare policies, ultimately enhancing the quality of care and outcomes for older adults.</p></sec></sec>
<sec id="s5">
<label>5</label>
<title>Conclusions</title>
<p>Discharge destination, comorbidities, geriatric syndrome, and frailty independently and interactively exerted a significant impact on post-hospitalization mortality risk among older adults. Discharged older adults with severe frailty or multiple geriatric syndromes had the greatest risk of mortality. Thus, individualized post-discharge management strategies targeting this particularly vulnerable population are urgently needed. Early identification of high-risk individuals and implementation of optimized transitional care may contribute to improved survival and quality of life in aging populations.</p></sec>
</body>
<back>
<sec sec-type="data-availability" id="s6">
<title>Data availability statement</title>
<p>The data analyzed in this study is subject to the following licenses/restrictions: this study was performed using the National Health Insurance System database (<ext-link ext-link-type="uri" xlink:href="https://nhiss.nhis.or.kr/en/z/a/001/lpza001m01en.do">https://nhiss.nhis.or.kr/en/z/a/001/lpza001m01en.do</ext-link>), and the results do not necessarily represent the opinions of the National Health Insurance Corporation. Restrictions apply to the availability of these data, which were used under the license for this study. Requests to access these datasets should be directed to National Health Insurance Corporation.</p>
</sec>
<sec sec-type="ethics-statement" id="s7">
<title>Ethics statement</title>
<p>The studies involving humans were approved by Institutional Review Board of Seoul National University Bundang Hospital. The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation was not required from the participants or the participants&#x00027; legal guardians/next of kin because this retrospective cohort study used population-based data from the National Health Insurance Service (NHIS) of South Korea. The requirement for informed consent was waived owing to the retrospective study design.</p>
</sec>
<sec sec-type="author-contributions" id="s8">
<title>Author contributions</title>
<p>SK: Writing &#x02013; original draft, Conceptualization, Visualization. J-rL: Writing &#x02013; review &#x00026; editing, Data curation, Formal analysis, Investigation. KK: Data curation, Formal analysis, Validation, Writing &#x02013; review &#x00026; editing. JP: Data curation, Investigation, Resources, Writing &#x02013; review &#x00026; editing. KL: Data curation, Formal analysis, Investigation, Writing &#x02013; review &#x00026; editing. HK: Data curation, Writing &#x02013; review &#x00026; editing. EC: Validation, Visualization, Writing &#x02013; review &#x00026; editing. HL: Conceptualization, Supervision, Writing &#x02013; review &#x00026; editing.</p>
</sec>
<sec sec-type="COI-statement" id="conf1">
<title>Conflict of interest</title>
<p>The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec sec-type="ai-statement" id="s10">
<title>Generative AI statement</title>
<p>The author(s) declared that generative AI was not used in the creation of this manuscript.</p>
<p>Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.</p></sec>
<sec sec-type="disclaimer" id="s11">
<title>Publisher&#x00027;s note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec><sec sec-type="supplementary-material" id="s12">
<title>Supplementary material</title>
<p>The Supplementary Material for this article can be found online at: <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fpubh.2026.1754972/full#supplementary-material">https://www.frontiersin.org/articles/10.3389/fpubh.2026.1754972/full#supplementary-material</ext-link></p>
<supplementary-material xlink:href="Table_1.docx" id="SM1" mimetype="application/vnd.openxmlformats-officedocument.wordprocessingml.document" xmlns:xlink="http://www.w3.org/1999/xlink"/></sec>
<ref-list>
<title>References</title>
<ref id="B1">
<label>1.</label>
<mixed-citation publication-type="web"><person-group person-group-type="author"><name><surname>Population</surname> <given-names>Projections</given-names></name></person-group>. <source>Statistics Korea</source> (<year>2025</year>). Available online at: <ext-link ext-link-type="uri" xlink:href="https://kosis.kr/statHtml/statHtml.do?sso=ok&#x00026;returnurl=https%3A%2F%2Fkosis.kr%3A443%2FstatHtml%2FstatHtml.do%3Flist_id%3D101_A0502%26obj_var_id%3D%26seqNo%3D%26eType%3D%26tblId%3DDT_1BPA002%26vw_cd%3DMT_TM1_TITLE%26orgId%3D101%26path%3D%252FeasyViewStatis%252FcustomStatisIndex.do%26conn_path%3DMT_TM1_TITLE%26itm_id%3D%26lang_mode%3Dko%26scrId%3D%26">https://kosis.kr/statHtml/statHtml.do?sso=ok&#x00026;returnurl=https%3A%2F%2Fkosis.kr%3A443%2FstatHtml%2FstatHtml.do%3Flist_id%3D101_A0502%26obj_var_id%3D%26seqNo%3D%26eType%3D%26tblId%3DDT_1BPA002%26vw_cd%3DMT_TM1_TITLE%26orgId%3D101%26path%3D%252FeasyViewStatis%252FcustomStatisIndex.do%26conn_path%3DMT_TM1_TITLE%26itm_id%3D%26lang_mode%3Dko%26scrId%3D%26</ext-link> (Accessed June 5, 2025).</mixed-citation>
</ref>
<ref id="B2">
<label>2.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Iijima</surname> <given-names>K</given-names></name> <name><surname>Arai</surname> <given-names>H</given-names></name> <name><surname>Akishita</surname> <given-names>M</given-names></name> <name><surname>Endo</surname> <given-names>T</given-names></name> <name><surname>Ogasawara</surname> <given-names>K</given-names></name> <name><surname>Kashihara</surname> <given-names>N</given-names></name> <etal/></person-group>. <article-title>Toward the development of a vibrant, super-aged society: the future of medicine and society in J Apan</article-title>. <source>Geriatr Gerontol Int.</source> (<year>2021</year>) <volume>21</volume>:<fpage>601</fpage>&#x02013;<lpage>13</lpage>. doi: <pub-id pub-id-type="doi">10.1111/ggi.14201</pub-id></mixed-citation>
</ref>
<ref id="B3">
<label>3.</label>
<mixed-citation publication-type="book"><collab>OECD</collab>. <source>The Economic Benefit of Promoting Healthy Ageing and Community Care, Oecd Health Policy Studies</source>. <publisher-loc>Paris</publisher-loc>: <publisher-name>OECD Publishing</publisher-name> (<year>2025</year>).</mixed-citation>
</ref>
<ref id="B4">
<label>4.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Wang</surname> <given-names>Y-C</given-names></name> <name><surname>Chou</surname> <given-names>M-Y</given-names></name> <name><surname>Liang</surname> <given-names>C-K</given-names></name> <name><surname>Peng</surname> <given-names>L-N</given-names></name> <name><surname>Chen</surname> <given-names>L-K</given-names></name> <name><surname>Loh</surname> <given-names>C-H</given-names></name></person-group>. <article-title>Post-acute care as a key component in a healthcare system for older adults</article-title>. <source>Ann Geriatr Med Res.</source> (<year>2019</year>) <volume>23</volume>:<fpage>54</fpage>. doi: <pub-id pub-id-type="doi">10.4235/agmr.19.0009</pub-id><pub-id pub-id-type="pmid">32743289</pub-id></mixed-citation>
</ref>
<ref id="B5">
<label>5.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Qian</surname> <given-names>XX</given-names></name> <name><surname>Chau</surname> <given-names>PH</given-names></name> <name><surname>Fong</surname> <given-names>DYT</given-names></name> <name><surname>Ho</surname> <given-names>M</given-names></name> <name><surname>Woo</surname> <given-names>J</given-names></name></person-group>. <article-title>Post-hospital falls among the older population: the temporal pattern in risk and healthcare burden</article-title>. <source>J Am Med Dir Assoc.</source> (<year>2023</year>) <volume>24</volume>:<fpage>1478</fpage>&#x02013;<lpage>83</lpage>.e2. doi: <pub-id pub-id-type="doi">10.1016/j.jamda.2023.07.014</pub-id><pub-id pub-id-type="pmid">37591487</pub-id></mixed-citation>
</ref>
<ref id="B6">
<label>6.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Krumholz</surname> <given-names>HM</given-names></name></person-group>. <article-title>Post-hospital syndrome&#x02013;a condition of generalized risk</article-title>. <source>N Engl J Med.</source> (<year>2013</year>) <volume>368</volume>:<fpage>100</fpage>. doi: <pub-id pub-id-type="doi">10.1056/NEJMp1212324</pub-id></mixed-citation>
</ref>
<ref id="B7">
<label>7.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Claridge</surname> <given-names>JA</given-names></name> <name><surname>Leukhardt</surname> <given-names>WH</given-names></name> <name><surname>Golob</surname> <given-names>JF</given-names></name> <name><surname>McCoy</surname> <given-names>AM</given-names></name> <name><surname>Malangoni</surname> <given-names>MA</given-names></name></person-group>. <article-title>Moving beyond traditional measurement of mortality after injury: evaluation of risks for late death</article-title>. <source>J Am Coll Surg.</source> (<year>2010</year>) 210:788&#x02013;<volume>94</volume>, <fpage>94</fpage>&#x02013;<lpage>6</lpage>. doi: <pub-id pub-id-type="doi">10.1016/j.jamcollsurg.2009.12.035</pub-id><pub-id pub-id-type="pmid">20421051</pub-id></mixed-citation>
</ref>
<ref id="B8">
<label>8.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Linder</surname> <given-names>W</given-names></name> <name><surname>Ssegonja</surname> <given-names>R</given-names></name> <name><surname>Feldman</surname> <given-names>I</given-names></name> <name><surname>Kristiansson</surname> <given-names>RS</given-names></name> <name><surname>Marchi</surname> <given-names>J</given-names></name> <name><surname>Winblad</surname> <given-names>U</given-names></name></person-group>. <article-title>Inter-organizational coordination to improve patient outcomes in multimorbid older patients following hospital discharge - a systematic review</article-title>. <source>Int J Integr Care.</source> (<year>2025</year>) <volume>25</volume>:<fpage>12</fpage>. doi: <pub-id pub-id-type="doi">10.5334/ijic.9018</pub-id><pub-id pub-id-type="pmid">40384960</pub-id></mixed-citation>
</ref>
<ref id="B9">
<label>9.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Springer</surname> <given-names>MV</given-names></name> <name><surname>Skolarus</surname> <given-names>LE</given-names></name> <name><surname>Feng</surname> <given-names>C</given-names></name> <name><surname>Burke</surname> <given-names>JF</given-names></name></person-group>. <article-title>Functional impairment and postacute care discharge setting may be useful for stroke survival prognostication</article-title>. <source>J Am Heart Assoc.</source> (<year>2022</year>) <volume>11</volume>:<fpage>e024327</fpage>. doi: <pub-id pub-id-type="doi">10.1161/JAHA.121.024327</pub-id><pub-id pub-id-type="pmid">35232223</pub-id></mixed-citation>
</ref>
<ref id="B10">
<label>10.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Lynch</surname> <given-names>EA</given-names></name> <name><surname>Labberton</surname> <given-names>AS</given-names></name> <name><surname>Kim</surname> <given-names>J</given-names></name> <name><surname>Kilkenny</surname> <given-names>MF</given-names></name> <name><surname>Andrew</surname> <given-names>NE</given-names></name> <name><surname>Lannin</surname> <given-names>NA</given-names></name> <etal/></person-group>. <article-title>Out of sight, out of mind: long-term outcomes for people discharged home, to inpatient rehabilitation and to residential aged care after stroke</article-title>. <source>Disabil Rehabil.</source> (<year>2022</year>) <volume>44</volume>:<fpage>2608</fpage>&#x02013;<lpage>14</lpage>. doi: <pub-id pub-id-type="doi">10.1080/09638288.2020.1852616</pub-id><pub-id pub-id-type="pmid">33307842</pub-id></mixed-citation>
</ref>
<ref id="B11">
<label>11.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Bra&#x000F1;as</surname> <given-names>F</given-names></name> <name><surname>Torralba</surname> <given-names>M</given-names></name> <name><surname>Antela</surname> <given-names>A</given-names></name> <name><surname>Vergas</surname> <given-names>J</given-names></name> <name><surname>Ram&#x000ED;rez</surname> <given-names>M</given-names></name> <name><surname>Ryan</surname> <given-names>P</given-names></name> <etal/></person-group>. <article-title>Effects of frailty, geriatric syndromes, and comorbidity on mortality and quality of life in older adults with Hiv</article-title>. <source>BMC Geriatr.</source> (<year>2023</year>) <volume>23</volume>:<fpage>4</fpage>. doi: <pub-id pub-id-type="doi">10.1186/s12877-022-03719-8</pub-id><pub-id pub-id-type="pmid">36597036</pub-id></mixed-citation>
</ref>
<ref id="B12">
<label>12.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Gijsen</surname> <given-names>R</given-names></name> <name><surname>Hoeymans</surname> <given-names>N</given-names></name> <name><surname>Schellevis</surname> <given-names>FG</given-names></name> <name><surname>Ruwaard</surname> <given-names>D</given-names></name> <name><surname>Satariano</surname> <given-names>WA</given-names></name> <name><surname>van den Bos</surname> <given-names>GA</given-names></name></person-group>. <article-title>Causes and consequences of comorbidity: a review</article-title>. <source>J Clin Epidemiol.</source> (<year>2001</year>) <volume>54</volume>:<fpage>661</fpage>&#x02013;<lpage>74</lpage>. doi: <pub-id pub-id-type="doi">10.1016/S0895-4356(00)00363-2</pub-id><pub-id pub-id-type="pmid">11438406</pub-id></mixed-citation>
</ref>
<ref id="B13">
<label>13.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Dorr</surname> <given-names>DA</given-names></name> <name><surname>Markwardt</surname> <given-names>S</given-names></name> <name><surname>Bobo</surname> <given-names>M</given-names></name> <name><surname>Allore</surname> <given-names>HG</given-names></name> <name><surname>Botoseneanu</surname> <given-names>A</given-names></name> <name><surname>Newsom</surname> <given-names>JT</given-names></name> <etal/></person-group>. <article-title>The extent and burden of high multimorbidity on older adults in the Us: a descriptive analysis of medicare beneficiaries</article-title>. <source>BMC Geriatr.</source> (<year>2024</year>) <volume>24</volume>:<fpage>777</fpage>. doi: <pub-id pub-id-type="doi">10.1186/s12877-024-05329-y</pub-id><pub-id pub-id-type="pmid">39304796</pub-id></mixed-citation>
</ref>
<ref id="B14">
<label>14.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Clegg</surname> <given-names>A</given-names></name> <name><surname>Young</surname> <given-names>J</given-names></name> <name><surname>Iliffe</surname> <given-names>S</given-names></name> <name><surname>Rikkert</surname> <given-names>MO</given-names></name> <name><surname>Rockwood</surname> <given-names>K</given-names></name></person-group>. <article-title>Frailty in elderly people</article-title>. <source>Lancet.</source> (<year>2013</year>) <volume>381</volume>:<fpage>752</fpage>&#x02013;<lpage>62</lpage>. doi: <pub-id pub-id-type="doi">10.1016/S0140-6736(12)62167-9</pub-id></mixed-citation>
</ref>
<ref id="B15">
<label>15.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Vetrano</surname> <given-names>DL</given-names></name> <name><surname>Foebel</surname> <given-names>AD</given-names></name> <name><surname>Marengoni</surname> <given-names>A</given-names></name> <name><surname>Brandi</surname> <given-names>V</given-names></name> <name><surname>Collamati</surname> <given-names>A</given-names></name> <name><surname>Heckman</surname> <given-names>GA</given-names></name> <etal/></person-group>. <article-title>Chronic diseases and geriatric syndromes: the different weight of comorbidity</article-title>. <source>Eur J Intern Med.</source> (<year>2016</year>) <volume>27</volume>:<fpage>62</fpage>&#x02013;<lpage>7</lpage>. doi: <pub-id pub-id-type="doi">10.1016/j.ejim.2015.10.025</pub-id><pub-id pub-id-type="pmid">26643938</pub-id></mixed-citation>
</ref>
<ref id="B16">
<label>16.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Lujic</surname> <given-names>S</given-names></name> <name><surname>Randall</surname> <given-names>DA</given-names></name> <name><surname>Simpson</surname> <given-names>JM</given-names></name> <name><surname>Falster</surname> <given-names>MO</given-names></name> <name><surname>Jorm</surname> <given-names>LR</given-names></name></person-group>. <article-title>Interaction effects of multimorbidity and frailty on adverse health outcomes in elderly hospitalised patients</article-title>. <source>Sci Rep.</source> (<year>2022</year>) <volume>12</volume>:<fpage>14139</fpage>. doi: <pub-id pub-id-type="doi">10.1038/s41598-022-18346-x</pub-id><pub-id pub-id-type="pmid">35986045</pub-id></mixed-citation>
</ref>
<ref id="B17">
<label>17.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Roller-Wirnsberger</surname> <given-names>R</given-names></name> <name><surname>Thurner</surname> <given-names>B</given-names></name> <name><surname>Pucher</surname> <given-names>C</given-names></name> <name><surname>Lindner</surname> <given-names>S</given-names></name> <name><surname>Wirnsberger</surname> <given-names>GH</given-names></name></person-group>. <article-title>The clinical and therapeutic challenge of treating older patients in clinical practice</article-title>. <source>Br J Clin Pharmacol.</source> (<year>2020</year>) <volume>86</volume>:<fpage>1904</fpage>&#x02013;<lpage>11</lpage>. doi: <pub-id pub-id-type="doi">10.1111/bcp.14074</pub-id><pub-id pub-id-type="pmid">31321798</pub-id></mixed-citation>
</ref>
<ref id="B18">
<label>18.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Avelino-Silva</surname> <given-names>TJ</given-names></name> <name><surname>Roma</surname> <given-names>MFB</given-names></name> <name><surname>Dutra</surname> <given-names>AF</given-names></name> <name><surname>Malheiro</surname> <given-names>A</given-names></name> <name><surname>Speranza</surname> <given-names>ACC</given-names></name> <name><surname>Casale</surname> <given-names>AM</given-names></name> <etal/></person-group>. <article-title>Geriatric syndromes and mortality among hospitalized older adults</article-title>. <source>JAMA Netw Open.</source> (<year>2026</year>) <volume>9</volume>:<fpage>e2555740</fpage>. <pub-id pub-id-type="pmid">41591773</pub-id></mixed-citation>
</ref>
<ref id="B19">
<label>19.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Heyl</surname> <given-names>J</given-names></name> <name><surname>Hardy</surname> <given-names>F</given-names></name> <name><surname>Tucker</surname> <given-names>K</given-names></name> <name><surname>Hopper</surname> <given-names>A</given-names></name> <name><surname>March&#x000E3;</surname> <given-names>MJ</given-names></name> <name><surname>Navaratnam</surname> <given-names>AV</given-names></name> <etal/></person-group>. <article-title>Frailty, comorbidity, and associations with in-hospital mortality in older Covid-19 patients: exploratory study of administrative data</article-title>. <source>Interact J Med Res.</source> (<year>2022</year>) <volume>11</volume>:<fpage>e41520</fpage>. doi: <pub-id pub-id-type="doi">10.2196/41520</pub-id><pub-id pub-id-type="pmid">36423306</pub-id></mixed-citation>
</ref>
<ref id="B20">
<label>20.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Boucher</surname> <given-names>EL</given-names></name> <name><surname>Gan</surname> <given-names>JM</given-names></name> <name><surname>Rothwell</surname> <given-names>PM</given-names></name> <name><surname>Shepperd</surname> <given-names>S</given-names></name> <name><surname>Pendlebury</surname> <given-names>ST</given-names></name></person-group>. <article-title>Prevalence and outcomes of frailty in unplanned hospital admissions: a systematic review and meta-analysis of hospital-wide and general (Internal) medicine cohorts</article-title>. <source>EClinicalMedicine.</source> (<year>2023</year>) <volume>59</volume>:<fpage>101947</fpage>. doi: <pub-id pub-id-type="doi">10.1016/j.eclinm.2023.101947</pub-id><pub-id pub-id-type="pmid">37138587</pub-id></mixed-citation>
</ref>
<ref id="B21">
<label>21.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Lee</surname> <given-names>H</given-names></name> <name><surname>Lee</surname> <given-names>J-r</given-names></name> <name><surname>Jung</surname> <given-names>H</given-names></name> <name><surname>Lee</surname> <given-names>JY</given-names></name></person-group>. <article-title>Power of universal health coverage in the era of Covid-19: a nationwide observational study</article-title>. <source>Lancet Reg Health West Pac.</source> (<year>2021</year>) <volume>7</volume>:<fpage>100088</fpage>. doi: <pub-id pub-id-type="doi">10.1016/j.lanwpc.2020.100088</pub-id><pub-id pub-id-type="pmid">33521744</pub-id></mixed-citation>
</ref>
<ref id="B22">
<label>22.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Glasheen</surname> <given-names>WP</given-names></name> <name><surname>Cordier</surname> <given-names>T</given-names></name> <name><surname>Gumpina</surname> <given-names>R</given-names></name> <name><surname>Haugh</surname> <given-names>G</given-names></name> <name><surname>Davis</surname> <given-names>J</given-names></name> <name><surname>Renda</surname> <given-names>A</given-names></name></person-group>. <article-title>Charlson comorbidity index: Icd-9 update and Icd-10 translation</article-title>. <source>Am Health Drug Benefits.</source> (<year>2019</year>) <volume>12</volume>:<fpage>188</fpage>. <pub-id pub-id-type="pmid">31428236</pub-id></mixed-citation>
</ref>
<ref id="B23">
<label>23.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Kim</surname> <given-names>S</given-names></name></person-group>. <article-title>Park Jh, Ahn H, Lee S, Yoo HJ, Yoo J, et al. Risk factors of geriatric syndromes in Korean population</article-title>. <source>Ann Geriatr Med Res</source>. (<year>2017</year>) <volume>21</volume>:<fpage>123</fpage>&#x02013;<lpage>30</lpage>. doi: <pub-id pub-id-type="doi">10.4235/agmr.2017.21.3.123</pub-id></mixed-citation>
</ref>
<ref id="B24">
<label>24.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Lai</surname> <given-names>H-Y</given-names></name> <name><surname>Huang</surname> <given-names>S-T</given-names></name> <name><surname>Chen</surname> <given-names>L-K</given-names></name> <name><surname>Hsiao</surname> <given-names>F-Y</given-names></name></person-group>. <article-title>Development of frailty index using Icd-10 codes to predict mortality and rehospitalization of older adults: an update of the multimorbidity frailty index</article-title>. <source>Arch Gerontol Geriatr.</source> (<year>2022</year>) <volume>100</volume>:<fpage>104646</fpage>. doi: <pub-id pub-id-type="doi">10.1016/j.archger.2022.104646</pub-id><pub-id pub-id-type="pmid">35183986</pub-id></mixed-citation>
</ref>
<ref id="B25">
<label>25.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Peng</surname> <given-names>LN</given-names></name> <name><surname>Hsiao</surname> <given-names>FY</given-names></name> <name><surname>Lee</surname> <given-names>WJ</given-names></name> <name><surname>Huang</surname> <given-names>ST</given-names></name> <name><surname>Chen</surname> <given-names>LK</given-names></name></person-group>. <article-title>Comparisons between hypothesis- and data-driven approaches for multimorbidity frailty index: a machine learning approach</article-title>. <source>J Med Internet Res.</source> (<year>2020</year>) <volume>22</volume>:<fpage>e16213</fpage>. doi: <pub-id pub-id-type="doi">10.2196/16213</pub-id><pub-id pub-id-type="pmid">32525481</pub-id></mixed-citation>
</ref>
<ref id="B26">
<label>26.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Liao</surname> <given-names>W-J</given-names></name> <name><surname>Lai</surname> <given-names>H-Y</given-names></name> <name><surname>Lin</surname> <given-names>L-Y</given-names></name> <name><surname>Wu</surname> <given-names>C-H</given-names></name> <name><surname>Hsiao</surname> <given-names>F-Y</given-names></name> <name><surname>Chen</surname> <given-names>L-K</given-names></name></person-group>. <article-title>Multimorbidity frailty index and clinical outcomes among 42,989 older heart failure patients directly discharged from emergency departments: a nationwide retrospective cohort study</article-title>. <source>Exp Gerontol.</source> (<year>2025</year>) <volume>205</volume>:<fpage>112754</fpage>. doi: <pub-id pub-id-type="doi">10.1016/j.exger.2025.112754</pub-id><pub-id pub-id-type="pmid">40239852</pub-id></mixed-citation>
</ref>
<ref id="B27">
<label>27.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Lee</surname> <given-names>H</given-names></name> <name><surname>Cho</surname> <given-names>J</given-names></name> <name><surname>Shin</surname> <given-names>DW</given-names></name> <name><surname>Lee</surname> <given-names>S-P</given-names></name> <name><surname>Hwang</surname> <given-names>S-S</given-names></name> <name><surname>Oh</surname> <given-names>J</given-names></name> <etal/></person-group>. <article-title>Association of cardiovascular health screening with mortality, clinical outcomes, and health care cost: a nationwide cohort study</article-title>. <source>Prevent Med.</source> (<year>2015</year>) <volume>70</volume>:<fpage>19</fpage>&#x02013;<lpage>25</lpage>. doi: <pub-id pub-id-type="doi">10.1016/j.ypmed.2014.11.007</pub-id><pub-id pub-id-type="pmid">25445334</pub-id></mixed-citation>
</ref>
<ref id="B28">
<label>28.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Kang</surname> <given-names>E</given-names></name> <name><surname>Yun</surname> <given-names>J</given-names></name> <name><surname>Hwang</surname> <given-names>S-H</given-names></name> <name><surname>Lee</surname> <given-names>H</given-names></name> <name><surname>Lee</surname> <given-names>JY</given-names></name></person-group>. <article-title>The impact of the Covid-19 pandemic in the healthcare utilization in Korea: analysis of a nationwide survey</article-title>. <source>J Infect Public Health.</source> (<year>2022</year>) <volume>15</volume>:<fpage>915</fpage>&#x02013;<lpage>21</lpage>. doi: <pub-id pub-id-type="doi">10.1016/j.jiph.2022.07.003</pub-id><pub-id pub-id-type="pmid">35872432</pub-id></mixed-citation>
</ref>
<ref id="B29">
<label>29.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Kim</surname> <given-names>H-J</given-names></name> <name><surname>Lee</surname> <given-names>J-R</given-names></name> <name><surname>Lee</surname> <given-names>H</given-names></name> <name><surname>Kim</surname> <given-names>J-S</given-names></name></person-group>. <article-title>Healthcare costs due to dizziness/vertigo in Korea: analyses using the public data of health insurance review &#x00026; assessment service</article-title>. <source>J Korean Med Sci.</source> (<year>2024</year>) <volume>39</volume>:<fpage>e214</fpage>. doi: <pub-id pub-id-type="doi">10.3346/jkms.2024.39.e214</pub-id></mixed-citation>
</ref>
<ref id="B30">
<label>30.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Ahluwalia</surname> <given-names>SC</given-names></name> <name><surname>Gross</surname> <given-names>CP</given-names></name> <name><surname>Chaudhry</surname> <given-names>SI</given-names></name> <name><surname>Ning</surname> <given-names>YM</given-names></name> <name><surname>Leo-Summers</surname> <given-names>L</given-names></name> <name><surname>Van Ness</surname> <given-names>PH</given-names></name> <etal/></person-group>. <article-title>Impact of comorbidity on mortality among older persons with advanced heart failure</article-title>. <source>J Gen Intern Med.</source> (<year>2012</year>) <volume>27</volume>:<fpage>513</fpage>&#x02013;<lpage>9</lpage>. doi: <pub-id pub-id-type="doi">10.1007/s11606-011-1930-3</pub-id><pub-id pub-id-type="pmid">22095572</pub-id></mixed-citation>
</ref>
<ref id="B31">
<label>31.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Nunes</surname> <given-names>BP</given-names></name> <name><surname>Flores</surname> <given-names>TR</given-names></name> <name><surname>Mielke</surname> <given-names>GI</given-names></name> <name><surname>Thum&#x000E9;</surname> <given-names>E</given-names></name> <name><surname>Facchini</surname> <given-names>LA</given-names></name></person-group>. <article-title>Multimorbidity and mortality in older adults: a systematic review and meta-analysis</article-title>. <source>Arch Gerontol Geriatr.</source> (<year>2016</year>) <volume>67</volume>:<fpage>130</fpage>&#x02013;<lpage>8</lpage>. doi: <pub-id pub-id-type="doi">10.1016/j.archger.2016.07.008</pub-id><pub-id pub-id-type="pmid">27500661</pub-id></mixed-citation>
</ref>
<ref id="B32">
<label>32.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>G&#x000F3;mez-Ramos</surname> <given-names>JJ</given-names></name> <name><surname>Gonz&#x000E1;lez-Guerra</surname> <given-names>M</given-names></name> <name><surname>D&#x000E1;valos-Rodr&#x000ED;guez</surname> <given-names>IP</given-names></name> <name><surname>P&#x000E9;rez-Ru&#x000ED;z</surname> <given-names>ME</given-names></name> <name><surname>Pe&#x000F1;a-Dur&#x000E1;n</surname> <given-names>E</given-names></name> <name><surname>Mar&#x000ED;n-Medina</surname> <given-names>A</given-names></name> <etal/></person-group>. <article-title>Geriatric syndromes and their relationship with mortality in a population of mexican older adults aged 65 and over, admitted to the emergency department of a second-level care hospital</article-title>. <source>Healthcare</source>. (<year>2024</year>) <volume>12</volume>:<fpage>1166</fpage>. doi: <pub-id pub-id-type="doi">10.3390/healthcare12121166</pub-id><pub-id pub-id-type="pmid">38921281</pub-id></mixed-citation>
</ref>
<ref id="B33">
<label>33.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Huang</surname> <given-names>C-C</given-names></name> <name><surname>Lee</surname> <given-names>J-D</given-names></name> <name><surname>Yang</surname> <given-names>D-C</given-names></name> <name><surname>Shih</surname> <given-names>H-I</given-names></name> <name><surname>Sun</surname> <given-names>C-Y</given-names></name> <name><surname>Chang</surname> <given-names>C-M</given-names></name></person-group>. <article-title>Associations between geriatric syndromes and mortality in community-dwelling elderly: results of a national longitudinal study in Taiwan</article-title>. <source>J Am Med Dir Assoc.</source> (<year>2017</year>) <volume>18</volume>:<fpage>246</fpage>&#x02013;<lpage>51</lpage>. doi: <pub-id pub-id-type="doi">10.1016/j.jamda.2016.09.017</pub-id><pub-id pub-id-type="pmid">27838338</pub-id></mixed-citation>
</ref>
<ref id="B34">
<label>34.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Abizanda</surname> <given-names>P</given-names></name> <name><surname>Romero</surname> <given-names>L</given-names></name> <name><surname>Sanchez-Jurado</surname> <given-names>P</given-names></name> <name><surname>Martinez-Reig</surname> <given-names>M</given-names></name> <name><surname>Alfonso-Silguero</surname> <given-names>S</given-names></name> <name><surname>Rodriguez-Manas</surname> <given-names>L</given-names></name></person-group>. <article-title>Age, frailty, disability, institutionalization, multimorbidity or comorbidity. Which are the main targets in older adults?</article-title> <source>J Nutr Health Aging.</source> (<year>2014</year>) <volume>18</volume>:<fpage>622</fpage>&#x02013;<lpage>7</lpage>. doi: <pub-id pub-id-type="doi">10.1007/s12603-014-0033-3</pub-id><pub-id pub-id-type="pmid">24950154</pub-id></mixed-citation>
</ref>
<ref id="B35">
<label>35.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Grabovac</surname> <given-names>I</given-names></name> <name><surname>Haider</surname> <given-names>S</given-names></name> <name><surname>Mogg</surname> <given-names>C</given-names></name> <name><surname>Majewska</surname> <given-names>B</given-names></name> <name><surname>Drgac</surname> <given-names>D</given-names></name> <name><surname>Oberndorfer</surname> <given-names>M</given-names></name> <etal/></person-group>. <article-title>Frailty status predicts all-cause and cause-specific mortality in community dwelling older adults</article-title>. <source>J Am Med Dir Assoc.</source> (<year>2019</year>) <volume>20</volume>:<fpage>1230</fpage>&#x02013;<lpage>5</lpage>.e2. doi: <pub-id pub-id-type="doi">10.1016/j.jamda.2019.06.007</pub-id><pub-id pub-id-type="pmid">31351859</pub-id></mixed-citation>
</ref>
<ref id="B36">
<label>36.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Magdon-Ismail</surname> <given-names>Z</given-names></name> <name><surname>Ledneva</surname> <given-names>T</given-names></name> <name><surname>Sun</surname> <given-names>M</given-names></name> <name><surname>Schwamm</surname> <given-names>LH</given-names></name> <name><surname>Sherman</surname> <given-names>B</given-names></name> <name><surname>Qian</surname> <given-names>F</given-names></name> <etal/></person-group>. <article-title>Factors Associated with 1-year mortality after discharge for acute stroke: what matters?</article-title> <source>Top Stroke Rehab</source>. (<year>2018</year>) <volume>25</volume>:<fpage>576</fpage>&#x02013;<lpage>83</lpage>. doi: <pub-id pub-id-type="doi">10.1080/10749357.2018.1499303</pub-id><pub-id pub-id-type="pmid">30281414</pub-id></mixed-citation>
</ref>
<ref id="B37">
<label>37.</label>
<mixed-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Covinsky</surname> <given-names>KE</given-names></name> <name><surname>Pierluissi</surname> <given-names>E</given-names></name> <name><surname>Johnston</surname> <given-names>CB</given-names></name></person-group>. <article-title>Hospitalization-associated disability: &#x0201C;She Was Probably Able to Ambulate, but I&#x00027;m Not Sure&#x0201D;</article-title>. <source>Jama.</source> (<year>2011</year>) <volume>306</volume>:<fpage>1782</fpage>&#x02013;<lpage>93</lpage>. doi: <pub-id pub-id-type="doi">10.1001/jama.2011.1556</pub-id><pub-id pub-id-type="pmid">22028354</pub-id></mixed-citation>
</ref>
<ref id="B38">
<label>38.</label>
<mixed-citation publication-type="book"><person-group person-group-type="author"><name><surname>Tian</surname> <given-names>W</given-names></name></person-group>. <source>An All-Payer View of Hospital Discharge to Postacute Care, 2013</source>. <publisher-loc>Healthcare Cost and Utilization Project (Hcup) Statistical Briefs Rockville (MD)</publisher-loc>: <publisher-name>Agency for Healthcare Research and Quality (US)</publisher-name> (<year>2016</year>). <pub-id pub-id-type="pmid">27441335</pub-id></mixed-citation>
</ref>
</ref-list>
<fn-group>
<fn fn-type="custom" custom-type="edited-by" id="fn0001">
<p>Edited by: <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/268618/overview">Jinghua Wang</ext-link>, Tianjin Neurological Institute, China</p>
</fn>
<fn fn-type="custom" custom-type="reviewed-by" id="fn0002">
<p>Reviewed by: <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/2091848/overview">Shoukang Zou</ext-link>, Chengdu No.4 People&#x00027;s Hospital, China</p>
<p><ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/3127515/overview">Qing-Qing Yang</ext-link>, Sixth People&#x00027;s Hospital of Nantong, China</p>
</fn>
</fn-group>
<fn-group>
<fn fn-type="abbr" id="abbr1"><label>Abbreviations:</label><p>aHR, Adjusted hazard ratios; CCI, Charlson comorbidity index; mFI, Multimorbidity frailty index; NHIS, National Health Insurance Service.</p></fn></fn-group>
</back>
</article>