SARS-CoV2 pandemic has caused nearly 7 million deaths worldwide to May 31, 2023 (1). Since its appearance, numerous studies have established clinical risk factors for infection, severity, and mortality to identify patients at risk to optimize management (2, 3). These risk factors vary depending on the outcomes studied, but for all the adverse outcomes for COVID-19, they include age, diabetes, hypertension, and overweight or obesity (4). Some studies have tried to establish a link between clinical risk for COVID-19 and socio-demographic data such as social deprivation, but these mostly used aggregate data, not allowing to study precisely the link between social deprivation at the individual level and the different outcomes of COVID-19 (4, 5). During the first wave, France, especially Paris and its suburbs, were particularly affected. France was ranked 3rd regarding the absolute number of deaths, after Italy and United Kingdom, from March 17 to April 29, 2020 (6). From March 2 to May 31, 2020, in France, all-cause mortality increased with +25,027 deaths compared to the expected number of deaths (7). Île-de-France (Paris and its suburbs) totalized the highest excess of deaths compared to other regions. In this area, the excess mortality from any cause from March 1 to April 30, 2020, was +124% in Seine-Saint-Denis department and +69.1% in Paris department (8). Yet, in Seine-Saint-Denis, the population is among the youngest in France but also one of the most socially deprived (9). In 1998, the French High Council for Public Health defined social deprivation as a social instability characterized by the loss of one or more of the securities, in particular that of employment, allowing individuals and families to assume their professional, family and social responsibilities and to enjoy their fundamental rights (10). It is related to employment, family activities, integration into the community, formal participation in social institutions, recreation and education (11). This is an important and yet understudied topic. Evidence strongly suggests an association between socioeconomic status and poorer various health outcomes, including infectious diseases mortality. Social deprivation depicts more specificities than socioeconomic status, as it is multidimensional and covers different aspects such as housing, social environment, and health care coverage. The Evaluation de la précarité et des inégalités de santé dans les centres d’examens de santé (EPICES) score is particularly used in France (12, 13). This score was first published in 2002 and is composed of 11 questions allowing to assess multiple dimensions of social deprivation (14). Health literacy is defined as the ability of an individual to gain access to, understand and use the information in ways to promote and maintain good health (15, 16). As social deprivation, it is a major topic and it is associated with poorer health outcomes (17). Data on the link between health literacy and COVID-19 adverse outcomes remain scarce, and further studies are highly required. The hypothesis of the present study was that social deprivation was associated with COVID-19 in hospitalized people. The main objective is to assess the link between social deprivation and COVID-19 disease in an underprivileged department of the greater Paris area. The secondary objectives explore the link between health literacy, clinical factors, and COVID-19.

Between March 1 and October 31, 2020, 131 cases and 228 controls were eligible for the study. Sixty-two potential cases (41 patients with cognitive impairment, 5 patients at the end of life, 8 refusals to participate in the study, 2 patients on high-flow nasal oxygen therapy, 5 patients living in an institution, and 1 healthcare professional) and 48 potential controls (23 patients with cognitive impairment, 2 patients at the end of life, 16 refusals to participate in the study, 1 patient on high-flow nasal oxygen therapy, 4 patients living in an institution, and 2 healthcare professionals) were excluded. Analyses were therefore performed on 249 subjects included, 69 cases and 180 controls (see Figure 1).

Table 1 shows socio-demographic and clinical characteristics known as risk factors for COVID-19. For the population study, 109 (44.1%) were aged 65 years and older and 148 (59.4%) were men. There was no significant difference between the two groups regarding age and sex due to matching. Cases were more likely to report sharing their home with infected COVID-19 people (16.2% vs. 3.9%, p = 0.002). One hundred thirty-seven patients were overweight or obese (56.6%) and cases were more likely to be obese or overweight compared to controls (72.7% vs. 50.6%, p = 0.03). There were fewer smokers among cases population compared to controls (5.8% vs. 23.9%, p = 0.002).

Table 2 shows socio-demographic, health literacy and social deprivation data explored in this study. Twenty-three cases (33.8%) were born in France while 78 (43.3%) were born in France among controls (p = 0.13). Among the 147 foreign-born patients, 34 (13.7%) were born in sub-Saharan Africa, and 56 (22.6%) were born in the Maghreb. Cases required more frequently an interpreter (23,1% vs. 9%, p = 0,0074). The health insurance coverage was not significantly different in the two groups. Cases were more often professionally active (39.1% vs. 22.2%) while controls were more often inactive for health reasons (0% vs. 11.7%, p = 0.003). The surface area per person living in the household was smaller in the cases (18.3 m²/person vs. 27.5 m²/person, p < 0.001). The level of health literacy between the two groups tended to be higher in the controls (p = 0.09). The median EPICES score for overall population was 43.2 (IQR 29.4–62.9). Social deprivation assessed by the EPICES score was 67.7% in cases and 77.1% in controls (p = 0.19).

Table 3 shows EPICES score items. Cases appeared to be in couples more often (62.3% vs. 48.9%) but the difference was not significant (p = 0.079). Cases were more likely to have gone on vacation in the past 12 months (58.8% vs. 40%, p = 0.01).

Table 4 shows crude and adjusted OR for COVID-19 in hospitalized patients. In the multivariate model, subjects aged 65 to 74 years (aOR = 4.36; CI95% [1.39–14.99]) and older than 75 years (aOR = 3.88; CI95% [1.04–15.6]) were at greater risk for COVID-19 in hospitalized patients. Subjects born in sub-Saharan Africa or overseas departments were not at increased risk (aOR = 0.96; CI95% [0.37–2.36]). Being active professionally was a risk factor for COVID-19 after adjustment (aOR = 5.53; CI95% [1.84–18.38]) compared with being retired or inactive for health reasons. Job-seeking subjects appeared to be at higher risk as well, but the difference was not significant (aOR = 2.29; CI95% [0.74–7.41]). Subjects with low health literacy level were at higher risk compared with those with higher levels (aOR = 2.61; CI95% [1.22–5.68]). Being overweight or obese was also a risk factor for COVID-19 (aOR = 2.34; CI95% [1.17–4.86]). Social deprivation assessed by the EPICES score was not associated with COVID-19 in hospitalized patients (aOR = 0.47; CI95% [0.21–1.01]).

In our case-control study in a hospitalized population, social deprivation assessed by the EPICES score was not associated with COVID-19 in hospitalized patients. Factors associated with COVID-19 were advanced age, being professionally active, surface area inferior to 25 m² per person, low health literacy level, and being overweight or obese.

The lack of association between social deprivation assessed by the EPICES score and COVID-19 in hospitalized patients can be explained by several hypotheses. First, this score has not been evaluated for migrant populations, which was the majority in our study (59% of foreign-born persons). For example, the question asked about vacation during the last 12 months might not reflect social deprivation in the same way for migrant populations, who may return to their country of birth despite financial difficulties, compared to non-migrant populations. These limitations had already been highlighted by various authors (18). Second, a very high level of social deprivation within the two groups of our study population, and a strong homogeneity in the study population, making it difficult to identify significant differences (13). Third, some items in the score measuring social interactions (living as a couple, going on vacations, leisure activities) may be protective factors for social deprivation within the EPICES score, but risk factors for COVID-19 specifically. Indeed, there is considerable evidence that social gatherings are risk factors for transmission of SARS-CoV2 (21). Furthermore, Shah et al. show in a meta-analysis that the highest secondary attack rate within a household corresponds to husbands or wives (22).

Other dimensions of social deprivation not explored by the EPICES score are associated with high social interactions. Our study is consistent with the literature on the subject such as promiscuity in the household or the pursuit of so-called “essential” work which does not permit home confinement (23, 24). Through the concept of syndemics, many authors have underlined difficulties of weighting risk factors of social deprivation in the COVID-19 outbreaks (25). Our work also highlights the problem of its measurement tool.

Our study shows an unknown association between health literacy level when dichotomized, and COVID-19 in hospitalized patients, independent of social deprivation, as shown in multivariate analyses. Health literacy is linked to literacy and entails people’s knowledge, motivation, and competence to access, understand, appraise, and apply health information in order to make judgments and take decisions in everyday life concerning healthcare, disease prevention and health promotion to maintain or improve quality of life during the life course (26). Single Item Literacy Screener was used for assessing health literacy, which is a validated score in the literature, mostly for its simplicity and its reproducibility, as it consists of a single question: “How often do you need to have someone help you when you read instructions, pamphlets, or other written material from your doctor or pharmacy?.” This way of assessment was more convenient in a public health crisis, working in a COVID-19 unit. In order to minimize response bias related to comprehension of the question, we excluded patients with cognitive impairment and used an interpreter for non-French speakers. However, a social conformity bias, inherent to this type of survey, may have been present.

Do et al. showed that healthcare professionals with higher health literacy had fewer symptoms related to COVID-19, but no virological documentation was performed (27). Some studies have shown a correlation between good health literacy level and the application of barrier gestures (28, 29). Health literacy’s definition underlines the importance of various skills during a health crisis, not only in terms of understanding and applying barrier gestures, but also in terms of identifying symptoms requiring urgent care and following treatment recommendations. It is possible that subjects with higher levels of health literacy are more able to acquire information from public authorities or health care personnel regarding the barrier gestures to be applied to limit the risks of infection.

Our study also found already well-established risk factors, including body mass index. The association between overweight and COVID-19 is particularly strong, and the results of our study are consistent with multiple data in the literature (30). This was not the case for hypertension and diabetes. The association between COVID-19 and conditions such as diabetes and hypertension appear to be established. It is possible that the strength of this association may be less important than the association between COVID-19 and higher BMI (31).

Many studies have showed an excess risk of infection in black and Asian populations, which can be explained by greater social deprivation in these populations. Data are often collected in an aggregate fashion, and may lead to a confounding bias (32–34). Furthermore, the link with mortality may be less clear (35). Skin color was not collected because ethnic statistics are prohibited in France. No excess risk of infection was found among people born in sub-Saharan Africa and in the French overseas departments and territories. These results are consistent with another study conducted in Paris suburbs which showed no association between country of birth and COVID-19 severity (36). This suggests that the heterogeneity of the results in the literature may be explained by the different approach to collecting data on ethnicity.

Despite the significant difference regarding the need for an interpreter in our univariate analysis, we did not include this variable in our multivariate model, preferring to select the country of birth. In our population, some foreign-born subjects learnt French language because they were living in France for some time, or already learnt French language before their arrival. To be consistent with data in the literature that focus on ethnicity or skin color, we believe that some subjects with a non-white ethnicity would not have been analyzed properly.

Our study had several limitations. First, our population was particularly socially deprived in both groups, making it more difficult to identify a difference. Despite the high prevalence of precarious subjects, some data emerged as significant after adjustment, such as low health literacy level or household surface area per person. Second, our study was monocentric, limiting the recruitment pool. Third, our population was recruited between the months of March and October 2020, corresponding to heterogeneous periods in terms of lockdown policies, barrier gesture performance, mask availability, or local or national incidence.

Our study is original because it combines clinical with socio-demographic data using original case-control design. We assessed the multidimensional aspect of social deprivation without limiting ourselves to simple administrative criteria such as salary or health insurance coverage. This is also one of the first study to our knowledge to assess the relationship between health literacy level and documented COVID-19. This assessment was done using an easy-to-use and reproducible tool. Low health literacy level was only significantly associated with COVID-19 when dichotomized. Health literacy remains a complex topic and further studies on this subject seem highly required.

In conclusion, these results highlight the difficulty in establishing the link between COVID-19 in hospitalized patients and social deprivation from data collected at the individual level and the difficulty of using and transposing scores in research. Other scores than EPICES have been used in other countries and they might not reflect the same dimensions of social deprivation. Moreover, these different scores can only be used in specific configurations, especially in terms of country, health system or specificities of various populations. However, thanks to an adjustment on socio-demographic and clinical data, our study makes it possible to free ourselves from certain possibly confounding factors. It makes it possible to determine the influence of certain factors such as precariousness, obesity, and level of literacy, in relation to COVID-19, while measuring their interdependence. However, it does not allow us to say whether these factors are cumulative, within the framework of a syndemic (37).

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by Ethics committee of the Avicenne Hospital (CLEA-2020-126). The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

CJ, OB, and JG designed the study. CJ and JG developed the questionnaire. LD and JG managed the data collection, oversaw the data collection and maintained the database, performed the statistical analyses, and drafted the first versions of the manuscript. All authors contributed to the article and approved the submitted version.