Risk of Severe Acute Respiratory Syndrome Coronavirus 2 Acquisition Is Associated With Individual Exposure but Not Community-Level Transmission

Background Transmission rates after exposure to a severe acute respiratory syndrome coronavirus 2 (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. Methods We examined risk factors for SARS-CoV-2 infection in a randomized controlled trial of hydroxychloroquine as postexposure prophylaxis. Study procedures included standardized questionnaires at enrollment and daily self-collection of midturbinate swabs for SARS-CoV-2 polymerase chain reaction testing. County-level incidence was modeled using federally sourced data. Relative risks and 95% confidence intervals were calculated using modified Poisson regression. Results Eighty-six of 567 (15.2%) household/social contacts and 12 of 122 (9.8%) healthcare worker contacts acquired SARS-CoV-2 infection. Exposure to 2 suspected index cases (vs 1) significantly increased risk for both household/social contacts (relative risk [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, vs <= 2 hours), but not for household/social contacts. County incidence did not impact risk. Conclusions In our study, increased exposure to SARS-CoV-2 within household or healthcare 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. In an analysis of cases of SARS-CoV-2 transmission in a postexposure prophylaxis trial, increased exposure to SARS-CoV-2 within household or healthcare settings led to higher risk of infection, but higher community incidence did not.

Automated summary

In this study, increased exposure to SARS-CoV-2 within household or healthcare settings led to a higher risk of infection, but higher community incidence did not. This highlights the importance of interventions to reduce transmission in close contact settings.