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BackgroundHouseholds are specific transmission settings, as they involve close and repeated contacts between individuals of different generations. Household surveys provide a unique opportunity to better understand SARS-CoV-2 transmission and the role of individual characteristics. Here, we assessed the risk of SARS-CoV-2 acquisition from household and community exposure according to age, family ties, and socioeconomic and living conditions using data from the nationwide population-based EpiCov cohort/ORCHESTRA collaboration in November-December 2020. MethodsA history of SARS-CoV-2 infection was defined by a positive Euroimmun Anti-SARS-CoV-2 ELISA IgG result in November-December 2020. We applied stochastic chain binomial models fitted to the final distribution of infections in households to data from 17,983 individuals [≥]5 years enrolled from 8,165 households. Models estimated the competing risks of being infected from community and household exposure. ResultsYoung adults aged 18-24 years had the highest risk of extra-household infection (8.9%, [95% credible interval, Crl]: 7.5 - 10.4), whereas the oldest (>75) and the youngest (6-10) had the lowest risk, 2.6% (1.8 - 3.5) and 3.4% (1.9 - 5.2), respectively. Extra-household infection was also independently associated with socioeconomic conditions. Within households, the probability of person-to-person transmission increased with age: 10.6% (5.0 - 17.9) among 6-10-year-olds to 43.1% (32.6 - 53.2) among 65-74-year-olds. It was higher between partners 29.9% (25.6 - 34.3) and from mother to child 29.1% (21.4 - 37.3) than between individuals related by other family ties. ConclusionIn 2020 in France, the main factors identified for extra-household infection were age and socioeconomic conditions. Intra-household infection mainly depended on age and family ties. Key MessagesO_LIYoung adults aged 18-24 years had the highest probability of extra-household SARS-Cov-2 acquisition over the year 2020: 8.9%, 95% credible interval (95%Crl) 7.5 - 10.4. C_LIO_LIThe probability of extra-household infection increased with family income and population density in the municipality of residence and was higher in the French regions most affected by the waves of SARS-CoV-2. C_LIO_LIWhen estimating the probability of person-to-person transmission of SARS-CoV-2, the 65-74 year-olds had the highest susceptibility, i.e. the highest probability of SARS-CoV-2 acquisition when exposed to an infected household member (22.1%, 16.4 - 28.2) C_LIO_LIThe probability of transmission was the highest between partners (29.9%, 25.6 - 34.3). The probability of transmission was higher from mother to child than from father to child: 29.1%, (21.4 - 37.3) and 14.0% (5.9 - 22.8), respectively. The probability of transmission from child to parent was higher from children <12 years than for older children: 11.8% (2.5 - 25.1) and 4.1% (0.9 - 9.0), respectively. C_LI
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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.
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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.
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Aim To estimate the seroprevalence of SARS-CoV-2 infection in May-June 2020 after the lockdown in adults living in three regions in France and to identify the associated risk factors. Methods Participants in a survey on COVID-19 from an existing consortium of three general adult population cohorts living in the Ile-de-France (IDF) or Grand Est (GE), two regions with high rate of COVID-19, or in the Nouvelle-Aquitaine (NA), with a low rate, were asked to take a dried-blood spot (DBS) for anti-SARS-CoV-2 antibodies assessment. The primary outcome was a positive anti-SARS-CoV-2 ELISA IgG result against the spike protein of the virus (ELISA-S). The secondary outcomes were a positive ELISA IgG against the nucleocapsid protein (ELISA-NP), anti-SARS-CoV-2 neutralizing antibodies titers >=40 (SN), and predicted positivity obtained from a multiple imputation model (MI). Prevalence estimates were adjusted using sampling weights and post-stratification methods. Findings Between May 4, 2020 and June 23, 2020, 16,000 participants were asked to provide DBS, and 14,628 were included in the analysis, 983 with a positive ELISA-S, 511 with a positive ELISA-NP, 424 with SN>=40 and 941 (Standard Deviation=31) with a positive MI. Adjusted estimates of seroprevalence (positive ELISA-S) were 10.0% (95%CI 9.1%;10.9%) in IDF, 9.0% (95%CI 7.7%; 10.2%) in GE and 3.1% (95%CI 2.4%; 3.7%), in NA. The adjusted prevalence of positive ELISA-NP, SN and MI were 5.7%, 5.0% and 10.0% in IDF, 6.0%, 4.3% and 8.6% in GE, and 0.6%, 1.3% and 2.5% in NA, respectively. A higher seroprevalence was observed in younger participants and when at least one child or adolescent lived in the same household. A lower seroprevalence was observed in smokers compared to non-smokers. Interpretation At the end of the lockdown the prevalence of anti-SARS-CoV-2 IgG or neutralizing antibodies remained low in the French adult population, even in regions with high reported rates of COVID-19.
