Tuberculosis (TB) remains a significant global health challenge (1). While the Republic of Korea (ROK) has drastically reduced the incidence from 5,168 cases per 100,000 in 1965 to 38 cases per 100,000 in 2023 (2, 3) and TB-related mortality has also shown marked improvement, critical public health challenges remain (3–5). TB is designated as a nationally notifiable disease under the Infectious Diseases Control and Prevention Act, mandating that all new diagnoses be reported to community health centers within 24 h (6). Established in 2000, the Korean National Tuberculosis Surveillance System (KNTSS) continuously monitors patient demographics, diagnostic outcomes, treatment modalities, and overall patient prognoses. Furthermore, the introduction of the Public-Private Mix (PPM) program in 2011, which emphasizes nurse-led patient monitoring, contributed to a substantial 43.2% reduction in TB-related deaths from 2013 to 2023 (5, 7).

Migrant communities represent particularly vulnerable groups in the ROK’s TB landscape. Although foreign-born individuals account for only 3.5% of the total population (8), they now contribute to more than 5% of annual TB cases, a significant increase from 0.3% in 2001 to 5.7% in 2023 (9, 10). Notably, Chinese nationals, especially Korean Chinese from northeastern China, account for nearly half of all TB cases among migrants (11, 12). Although the general population in the ROK experienced a decline in LTFU—from 5.3% in 2011 to 2.4% in 2018 (13, 14)—migrant populations continue to face disproportionately high risks (12). Interestingly, although migrants had lower overall odds of treatment success (odds ratio [OR] 0.71, 95% confidence interval [CI] 0.46–1.12), this difference was not statistically significant. However, migrants demonstrate lower rates of treatment completion, as verified through microbiological confirmation, suggesting that despite effective initial therapy, disengagement often occurs during the continuation phase (12).

Migrant patients with TB face multifaceted barriers to continuing treatment (15). Socioeconomic challenges—including financial constraints, unstable employment, and housing insecurity—often intersect with healthcare system obstacles such as limited access to specialized PPM nurses (16–18). In addition, clinical factors such as drug-resistant TB and comorbid conditions such as diabetes and cancer further increase the risk of LTFU (12, 19–22). Despite the growing recognition of these challenges, the specific determinants of LTFU among migrant populations in the ROK remain underexplored. This study addresses this gap by analyzing TB cases among migrants reported to the KNTSS between 2016 and 2018 and comparing them with native TB cases to identify key risk factors for treatment discontinuation. Complementary in-depth interviews with PPM nurses working in regions with large migrant populations provided additional insights into the unique barriers faced by these patients.

This mixed method study was designed to investigate the factors affecting non-adherence and LTFU from TB treatment among foreign migrants in ROK, comparing them to native Korean TB patients. The study combined a retrospective cohort analysis of national health system data with complementary qualitative interviews.

This study offers crucial insights into the significant challenge of TB treatment adherence among foreign migrants in ROK, revealing a substantially higher rate of LTFU compared to native Korean patients. Despite comprising only 3.5% of the total population, foreign migrants accounted for over 5% of annual TB cases between 2016 and 2018, with an average incidence rate of 178.2 per 100,000, approximately 2.5 times higher than the national average. This disproportionate burden highlights an urgent need for targeted interventions.

The follow-up discontinuation rate among migrant patients with TB was significantly higher (21.5%) than that among domestic patients (2.3%). This significant disparity poses a critical barrier to global TB elimination efforts (26, 27). Previous research indicates that migration itself increases the likelihood of treatment discontinuation, with foreign nationals showing a higher tendency to disengage from care (19, 28). The mixed-methods approach utilized in this study provided a comprehensive understanding of the various determinants contributing to this issue. Several sociodemographic factors were found to profoundly influence LTFU among migrants.

Nationality emerged as a critical determinant of LTFU, with higher discontinuation rates seen among those from Thailand, Mongolia, and Vietnam compared to Chinese nationals. These elevated rates may partially due to systemic misclassification; Many migrants leave ROK for further care without formal transfer procedures, resulting in delayed immigration verification and erroneous classification as LTFU. Previous studies have similarly found that patients who depart without notifying health staff are flagged as LTFU once their exit is confirmed (19). Migrants with repeated treatment interruptions are often prioritized for deportation once non-infectious, contributing to higher discontinuation rates compared to residents.

Living arrangement also strongly influenced follow-up adherence. Migrants in single-person or non-family households were more likely to discontinue care than those living with their families, reflecting a lack of social and emotional support, less favorable living conditions, and limited access to healthcare (29, 30). Family presence is widely recognized as a protective factor, promoting adherence through motivation and oversight for medication adherence (31). Additional barriers—such as stigma, psychological distress, and insufficient treatment support—further hinder continuity of care for individuals living alone or in non-family environments (32, 33). Integration of housing support programs with local social welfare services has demonstrated effectiveness in mitigating risks such as drug-resistant TB, relapse, and mortality, ultimately improving overall treatment outcomes (28, 34).

The analysis identified a consistent gender disparity in TB treatment adherence, with female sex associated with lower odds of LTFU in both univariable (OR 0.73) and multivariate (aOR 0.83) models. This suggests that sex-specific factors may shape adherence patterns. Migrant females were more likely to live with family (47.8%) than males (29.3%), while males predominantly lived alone (59.5%). Since family support plays a key role in promoting medication adherence through emotional and practical support, this difference in living arrangements likely contributes to the disparity. Additionally, females reported lower smoking rates (95.3% non-smokers) versus males (37.5% current, 17.7% former smokers), indicating healthier behaviors that may support treatment completion. Females were also more often enrolled in the PPM program (58.5% vs. 49.2%), enhancing their access to structured nurse-led monitoring. These overlapping factors—social support, lifestyle, and program engagement—underscore the multifaceted gendered influences on treatment outcomes.

Clinical factors also contributed to the high LTFU rates. Drug-resistant TB significantly increased the risk of treatment discontinuation, with affected patients being 4.43 times more likely to be LTFU than those with drug-susceptible TB. The extended treatment duration, often triple that of standard regimens, and the severe side effects of second-line drugs contributes to voluntary interruption (35). These challenges underscore the need for enhanced adherence strategies, including continuous monitoring, comprehensive patient education, as well as targeted support for those with drug-resistant TB (12, 36, 37). While less common among migrants than natives, the presence of comorbidities such as diabetes and cancer significantly increased the odds of LTFU for migrants. This highlights the need for integrated care that addresses co-existing health conditions, a point also recognized in the National TB Management Guidelines which list diabetes and cancer as high-risk factors for TB progression (38).

Crucial systemic and health system factors were also identified. Migrants who experienced one or more care transfers were significantly more likely to be LTFU. This indicates that frequent transfers disrupt treatment continuity due to delays in record sharing, inconsistent protocols, and insufficient communication (39). Also, migrants had less access to PPM nurses (52.9%) compared to native Koreans (73.9%). PPM nurses are crucial for patient management, including initial investigations for reported patients and conducting vulnerability assessments for customized care (19, 40). The qualitative findings revealed that this disparity was compounded by low awareness among migrants of the availability of free TB treatment under the PPM program, leading to perceived costs at non-PPM facilities and avoidance of follow-up.

PPM nurses reported that many migrants perceived TB as a “mild cold” and prematurely discontinued treatment once symptoms improved, and are unaware of the significant risks associated with incomplete care, such as the development of drug-resistant TB and the possibility of relapse (31, 41). This underscores the urgent need for culturally and linguistically tailored educational campaigns that clearly explain TB’s severity, the importance of completing the full treatment course, and the risks of drug resistance and relapse (41–43). The qualitative data also highlighted significant language barriers and limitations of non-medical interpreters in effectively explaining complex medical information, such as drug side effects and regimen complexities. Improving medical interpretation services with trained professionals possessing specialized healthcare and TB-related knowledge is crucial to bridge these communication gaps.

These findings resonate with existing literature emphasizing that patient education, robust social support, and accessible, consistent care are fundamental to improving TB treatment adherence (19, 31). The study’s insights reinforce that overcoming high LTFU rates among migrant TB patients in the ROK necessitates a multi-faceted approach that extends beyond clinical management to address underlying social, cultural, and systemic barriers. This implies the need for proactive outreach, culturally sensitive health education, strengthened interpreter services, and policy reforms to ensure seamless, affordable, and comprehensive care for this vulnerable population. The “Tuberculosis Relief Belt” initiative represents a positive step in strengthening patient referral systems and providing financial subsidies to vulnerable groups, including support for treatment costs, outsourced medical expenses, caregiving, nutrition, and patient transport (28, 38).

While this study offers valuable insights, it is important to acknowledge its limitations. The authors themselves noted the lack of detailed clinical data, such as lung X-rays or smear/culture data, which could have made the study more robust. Similarly, the absence of detailed socioeconomic indicators (e.g., visa type, specific occupation, income, education level) limited a more nuanced understanding of disease progression and socioeconomic vulnerabilities. Additionally, the small sample size of multidrug-resistant cases restricted a thorough examination of its specific association with LTFU. Future research should aim to incorporate these variables for a more complete understanding.