Risk factors for community and intra-household transmission of SARS-Cov-2: a modelling study in the French national population-based EpiCov cohort.

We assessed the risk of SARS-CoV-2 acquisition from household and community exposure according to age, family ties, socioeconomic and living conditions using serological data from the nationwide population-based EpiCov cohort (ORCHESTRA collaboration). A 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 >6 years enrolled from 8,165 households. Models estimated the competing risks of being infected from community and household exposure. The 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 years) had the lowest risk, 2.6% (1.8, 3.5) and 3.4% (1.9, 5.2), respectively. Extra-household infection was also 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. In 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.