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- Title
Income differences in COVID-19 incidence and severity in Finland among people with foreign and native background: A population-based cohort study of individuals nested within households.
- Authors
Saarinen, Sanni; Moustgaard, Heta; Remes, Hanna; Sallinen, Riikka; Martikainen, Pekka
- Abstract
Background: Although intrahousehold transmission is a key source of Coronavirus Disease 2019 (COVID-19) infections, studies to date have not analysed socioeconomic risk factors on the household level or household clustering of severe COVID-19. We quantify household income differences and household clustering of COVID-19 incidence and severity. Methods and findings: We used register-based cohort data with individual-level linkage across various administrative registers for the total Finnish population living in working-age private households (N = 4,315,342). Incident COVID-19 cases (N = 38,467) were identified from the National Infectious Diseases Register from 1 July 2020 to 22 February 2021. Severe cases (N = 625) were defined as having at least 3 consecutive days of inpatient care with a COVID-19 diagnosis and identified from the Care Register for Health Care between 1 July 2020 and 31 December 2020. We used 2-level logistic regression with individuals nested within households to estimate COVID-19 incidence and case severity among those infected. Adjusted for age, sex, and regional characteristics, the incidence of COVID-19 was higher (odds ratio [OR] 1.67, 95% CI 1.58 to 1.77, p < 0.001, 28.4% of infections) among individuals in the lowest household income quintile than among those in the highest quintile (18.9%). The difference attenuated (OR 1.23, 1.16 to 1.30, p < 0.001) when controlling for foreign background but not when controlling for other household-level risk factors. In fact, we found a clear income gradient in incidence only among people with foreign background but none among those with native background. The odds of severe illness among those infected were also higher in the lowest income quintile (OR 1.97, 1.52 to 2.56, p < 0.001, 28.0% versus 21.6% in the highest quintile), but this difference was fully attenuated (OR 1.08, 0.77 to 1.52, p = 0.64) when controlling for other individual-level risk factors—comorbidities, occupational status, and foreign background. Both incidence and severity were strongly clustered within households: Around 77% of the variation in incidence and 20% in severity were attributable to differences between households. The main limitation of our study was that the test uptake for COVID-19 may have differed between population subgroups. Conclusions: Low household income appears to be a strong risk factor for both COVID-19 incidence and case severity, but the income differences are largely driven by having foreign background. The strong household clustering of incidence and severity highlights the importance of household context in the prevention and mitigation of COVID-19 outcomes. Sanni Saarinen and colleagues explore the association between income differences and COVID-19 incidence and severity among people with foreign and native background in Finland. Author summary: Why was this study done?: Large body of evidence indicates a higher risk for Coronavirus Disease 2019 (COVID-19) infection, severity, and mortality among people with low socioeconomic position. However, little is known about the reasons for this. Furthermore, the quality of the existing evidence is hampered by data limitations such as nonrepresentative samples and area-level measurement of socioeconomic position. Even though intrahousehold transmission is a significant source of COVID-19 infections, studies to date have not analysed socioeconomic risk factors at the household-level or the household clustering of severe COVID-19. What did the researchers do and find?: In a population-based cohort study (n = 4.3 M) from Finland, we showed that both COVID-19 incidence and case severity are higher in low-income households, but that the income differences are largely driven by other household- and individual-level risk factors. The increased risk of COVID-19 infection in low-income households was only present among people with foreign background and nonexistent among those with a native background. COVID-19 incidence and case severity are both strongly clustered within households: 77% of variation in incidence and 20% in case severity were attributable to differences between households. What do these findings mean?: Low household income is not an independent risk factor for COVID-19 outcomes among people with a native background. However, people with foreign background living in low-income households are particularly vulnerable and should be considered for targeted preventive measures. The strong household clustering of COVID-19 incidence and severity highlights the importance of the household context in understanding the microlevel dynamics of the COVID-19 pandemic.
- Subjects
FINLAND; INCOME; COVID-19; INDIGENOUS peoples; COVID-19 pandemic; REPORTING of diseases; CORONAVIRUS diseases
- Publication
PLoS Medicine, 2022, Vol 19, Issue 8, p1
- ISSN
1549-1277
- Publication type
Article
- DOI
10.1371/journal.pmed.1004038