Social Distancing, Mask Use, and Transmission of Severe Acute Respiratory Syndrome Coronavirus 2, Brazil, April-June 2020.

We assessed the associations of social distancing and mask use with symptomatic, laboratory-confirmed severe acute respiratory syndrome coronavirus 2 infection in Porto Alegre, Brazil. We conducted a population-based case-control study during April-June 2020. Municipal authorities furnished case-patients, and controls were taken from representative household surveys. In adjusted logistic regression analyses of 271 case-patients and 1,396 controls, those reporting moderate to greatest adherence to social distancing had 59% (odds ratio [OR] 0.41, 95% CI 0.24-0.70) to 75% (OR 0.25, 95% CI 0.15-0.42) lower odds of infection. Lesser out-of-household exposure (vs. going out every day all day) reduced odds from 52% (OR 0.48, 95% CI 0.29-0.77) to 75% (OR 0.25, 95% CI 0.18-0.36). Mask use reduced odds of infection by 87% (OR 0.13, 95% CI 0.04-0.36). In conclusion, social distancing and mask use while outside the house provided major protection against symptomatic infection.