RESUMO
BackgroundWe aimed to study whether social patterns of exposure to SARS-CoV-2 infection changed in France throughout the year 2020, in light to the easing of social contact restrictions. MethodsA population-based cohort of individuals aged 15 years or over was randomly selected from the national tax register to collect socio-economic data, migration history, and living conditions in May and November 2020. Home self-sampling on dried blood was proposed to a 10% random subsample in May and to all in November. A positive anti-SARS-CoV-2 ELISA IgG result against the virus spike protein (ELISA-S) was the primary outcome. The design, including sampling and post-stratification weights, was taken into account in univariate and multivariate analyses. ResultsOf the 134,391 participants in May, 107,759 completed the second questionnaire in November, and respectively 12,114 and 63,524 were tested. The national ELISA-S seroprevalence was 4.5% [95%CI: 4.0%-5.1%] in May and 6.2% [5.9%-6.6%] in November. It increased markedly in 18-24-year-old population from 4.8% to 10.0%, and among second-generation immigrants from outside Europe from 5.9% to 14.4%. This group remained strongly associated with seropositivity in November, after controlling for any contextual or individual variables, with an adjusted OR of 2.1 [1.7-2.7], compared to the majority population. In both periods, seroprevalence remained higher in healthcare professions than in other occupations. ConclusionThe risk of Covid-19 infection increased among young people and second-generation migrants between the first and second epidemic waves, in a context of less strict social restrictions, which seems to have reinforced territorialized socialization among peers.
RESUMO
Backgroundthe EpiCov study, initiated at the end of the first national lockdown in France, aimed to provide national and regional estimates of the seroprevalence of SARS-CoV-2 infection, and to analyze relations between living conditions and the dynamics of the epidemic. We present and discuss here the survey methodology, and describe the first-round fieldwork. Method371,000 individuals aged 15 years or more were randomly selected from the national tax register, stratified by departments, including three overseas departments, and by poverty level with over-representation of people living below the poverty line. Health, socio-economics, migration history, and living conditions were collected through self-computed-assisted web interviews or via computer-assisted telephone interviews. The first-round survey was conducted in May. A random subsample was eligible to receive material for home blood self-sample on dried blood spot (DBS), in order to detect IgG antibodies against the spike protein (Euroimmun ELISA-S), and neutralizing antibodies for non-negative ELISA-S. For the second-round conducted in November, all respondents were eligible for the antibodies detection from home DBS sample, as well as the other household members aged 6 years or more for 20% of them. Participation and adjustment for nonresponse134,391 respondents completed the first-round questionnaire from May 2 to June 1, 2020, including 16,970 (12.6%) respondents under the poverty line. Multimodal web/tel interviews was randomly assigned to 20% of the sample. The other were assigned to exclusive CAWI. Overall 17,441 respondents were eligible for home blood sample, among them 12,114 returned the DBS (interquartile date: May 25-June 5). The response probability was first estimated from logit models adjusted on a wide range of auxiliary demographic and socio-economic variables available from the sampling frame, and final weights calibrated to the margins of the population census permitted to correct for a large part of the non-response bias. ConclusionThe Epicov study is one of the largest national random population-based seroprevalence cohort, with both an epidemiological and sociological approaches to evaluate the spread of the COVID-19 epidemic, and the impact on health and living conditions. One of the major interests of this study is the broad coverage of the socio-economic and territorial diversity of the population.
