Risk of SARS-CoV-2 acquisition is associated with individual exposure but not community-level transmission

Transmission rates after exposure to a SARS-COV-2-positive individual within households and healthcare settings varies significantly between studies. Variability in the extent of exposure and community SARS-CoV-2 incidence may contribute to differences in observed rates. We examined risk factors for SARS-CoV-2 infection in a randomized controlled trial of hydroxychloroquine as post-exposure prophylaxis. Study procedures included standardized questionnaires at enrollment and daily self-collection of mid-turbinate swabs for SARS-CoV-2 PCR testing. County-level incidence was modeled using federally sourced data. Relative risks and 95% confidence intervals were calculated using modified Poisson regression. 86/567 (15.2%) of household/social contacts and 12/122 (9.8%) of healthcare worker contacts acquired SARS-CoV-2 infection. Exposure to two suspected index cases (versus one) significantly increased risk for both household/social contacts (RR 1.86) and healthcare workers (RR 8.18). Increased contact time also increased risk for healthcare workers (3-12 hours: RR 7.82, >12 hours: RR 11.81, versus ≤2 hours), but not for household/social contacts. County incidence did not impact risk. In our study, increased exposure to SARS-CoV-2 within household or health care settings led to higher risk of infection, but elevated community incidence did not. This reinforces the importance of interventions to decrease transmission in close contact settings.