SARS-CoV-2 incidence and risk factors in a national, community-based prospective cohort of U.S. adults

BACKGROUND: Epidemiologic risk factors for incident SARS-CoV-2 infection as determined via prospective cohort studies greatly augment and complement information from case-based surveillance and cross-sectional seroprevalence surveys. METHODS: We estimated the incidence of SARS-CoV-2 infection and risk factors in a well-characterized, national prospective cohort of 6,738 U.S. adults, enrolled March-August 2020, a subset of whom (n=4,510) underwent repeat serologic testing between May 2020 and January 2021. We examined the crude associations of sociodemographic factors, epidemiologic risk factors, and county-level community transmission with the incidence of seroconversion. In multivariable Poisson models we examined the association of social distancing and a composite score of several epidemiologic risk factors with the rate of seroconversion. FINDINGS: Among the 4,510 individuals with at least one serologic test, 323 (7.3%, 95% confidence interval [CI] 6.5%−8.1%) seroconverted by January 2021. Among 3,422 participants seronegative in May-September 2020 and tested during November 2020-January 2021, we observed 161 seroconversions over 1,646 person-years of follow-up (incidence rate of 9.8 per 100 person-years [95%CI 8.3–11.5]). In adjusted models, participants who reported always or sometimes social distancing with people they knew (IRR(always vs. never) 0.43, 95%CI 0.21–1.0; IRR(sometimes vs. never) 0.47, 95%CI 0.22–1.2) and people they did not know (IRR(always vs. never) 0.64, 95%CI 0.39–1.1; IRR(sometimes vs. never) 0.60, 95%CI 0.38–0.97) had lower rates of seroconversion. The rate of seroconversion increased across tertiles of the composite score of epidemiologic risk (IRR(medium vs. low) 1.5, 95%CI 0.92–2.4; IRR(high vs. low) 3.0, 95%CI 2.0–4.6). Among the 161 observed seroconversions, 28% reported no symptoms of COVID-like illness (i.e., were asymptomatic), and 27% reported a positive SARS-CoV-2 diagnostic test. Ultimately, only 29% reported isolating and 19% were asked about contacts. INTERPRETATION: Modifiable epidemiologic risk factors and poor reach of public health strategies drove SARS-CoV-2 transmission across the U.S during May 2020-January 2021. FUNDING: U.S. National Institutes of Allergy and Infectious Diseases (NIAID).