Risk Factors for Community and Intrahousehold Transmission of SARS-CoV-2: Modeling in a Nationwide French Population-Based Cohort Study, the EpiCoV Study

Abstract

We assessed the risk of acquiring severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from household and community exposure according to age, family ties, and socioeconomic and living conditions using serological data from a nationwide French population-based cohort study, the Epidémiologie et Conditions de Vie (EpiCoV) Study. A history of SARS-CoV-2 infection was defined by a positive anti-SARS-CoV-2 enzyme-linked immunosorbent assay immunoglobulin G result in November-December 2020. We applied stochastic chain binomial models fitted to the final distribution of household infections to data from 17,983 individuals aged ≥6 years from 8,165 households. Models estimated the competing risks of being infected from community and household exposure. The age group 18-24 years had the highest risk of extrahousehold infection (8.9%, 95% credible interval (CrI): 7.5, 10.4), whereas the oldest (≥75 years) and youngest (6-10 years) age groups had the lowest risk, at 2.6% (95% CrI: 1.8, 3.5) and 3.4% (95% CrI: 1.9, 5.2), respectively. Extrahousehold infection was also associated with socioeconomic conditions. Within households, the probability of person-to-person transmission increased with age, from 10.6% (95% CrI: 5.0, 17.9) among children aged 6-10 years to 43.1% (95% CrI: 32.6, 53.2) among adults aged 65-74 years. Transmission was higher between partners (29.9%, 95% CrI: 25.6, 34.3) and from mother to child (29.1%, 95% CrI: 21.4, 37.3) than between individuals related by other family ties. In 2020 in France, the main factors identified for extrahousehold SARS-CoV-2 infection were age and socioeconomic conditions. Intrahousehold infection mainly depended on age and family ties.

Keywords: COVID-19; SARS-CoV-2; coronavirus disease 2019; disease transmission; households; population-based surveys; seroprevalence; severe acute respiratory syndrome coronavirus 2.

Figure 1

Enrollment of participants in the EpiCoV Study and its household substudy, 2020. EpiCoV, Epidémiologie et Conditions de Vie; FOD, French overseas departments.

Figure 2

Characteristics of participants in the household substudy of the EpiCoV Study, 2020. A) SARS-CoV-2 seroprevalence (bars show 95% confidence intervals (CIs)) according to sex. The analysis included 8,674 males and 9,293 females. B) SARS-CoV-2 seroprevalence (bars, 95% CIs) according to age. Numbers of individuals by age group: ages 6–10 years, n = 632; ages 11–14 years, n = 832; ages 15–17 years, n = 745; ages 18–24 years, n = 1,797; ages 25–34 years, n = 1,304; ages 35–44 years, n = 1,513; ages 45–54 years, n = 3,100; ages 55–64 years, n = 3,601; ages 65–74 years, n = 3,244; ages ≥75 years, n = 1,215. C) Proportion of infected households (i.e., households with at least 1 positive case) according to household size. The overall number of households was 8,165. Numbers of households by household size: 1 person, n = 2,116; 2 people, n = 3,870; 3 people, n = 941; 4 people, n = 937; ≥5 people, n = 301. D) Among infected households (i.e., households with at least 1 positive case), total number of positive individuals in the household according to the size of the household. For example, among 3-member infected households, 67% had only 1 positive household member, 25% had 2 positive members, and 8% had 3 positive members. The overall number of infected households was 784. Numbers of infected households by household size: 1 person, n = 66; 2 people, n = 120; 3 people, n = 302; 4 people, n = 124; ≥5 people, n = 172. EpiCoV, Epidémiologie et Conditions de Vie; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Figure 3

Estimated probabilities (median values with 95% credible intervals (bars)) of extra- and intrahousehold SARS-CoV-2 infection, by age, in the household substudy of the EpiCoV Study, 2020. A) Estimated probability of infection from extrahousehold exposure according to the age of the susceptible individual. B) Estimated probability of infection from 1 single infected household member according to the age of the susceptible. C) Estimated probability of infection from 1 single infected household member according to the age of the infector. EpiCoV, Epidémiologie et Conditions de Vie; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Figure 4

Estimated probability (median values with 95% credible intervals (bars)) of person-to-person SARS-CoV-2 transmission according to A) household size and B) family ties (type of transmission) in the household substudy of the EpiCoV Study, 2020. EpiCoV, Epidémiologie et Conditions de Vie; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Figure 5

Estimated proportion of SARS-CoV-2 infections (median values with 95% credible intervals (bars)) that occurred within a household, according to household size, in the household substudy of the EpiCoV Study, 2020. EpiCoV, Epidémiologie et Conditions de Vie; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.