We evaluated the effectiveness of personal protective measures, including mask-wearing, handwashing, and social distancing, against COVID-19 infection among contacts of cases. We conducted a case-control study with 211 cases and 839 non-matched controls using all contact tracing records of Thailand's national Surveillance and Rapid Response Team. Cases were asymptomatic contacts of COVID-19 patients identified between 1 and 31 March 2020 who were diagnosed with COVID-19 by 21 April 2020; controls were asymptomatic contacts who were not diagnosed with COVID-19. Participants were queried about practices during contact periods with a case. Adjusted odds ratios (aOR) and 95% confidence intervals (CI) were estimated for associations between diagnosis of COVID-19 and covariates using multivariable logistic regression models. Wearing masks all the time during contact was independently associated with lower risk of COVID-19 infection compared to not wearing masks (aOR 0.23, 95% CI 0.09-0.60), while sometimes wearing masks during contact was not (aOR 0.87, 95% CI 0.41-1.84). Maintaining at least 1 meter distance from a COVID patient (aOR 0.15, 95% CI 0.04-0.63), duration of close contact [â¤]15 minutes versus longer (aOR 0.24, 95% CI 0.07-0.90), and handwashing often (aOR 0.34, 95% CI 0.13-0.87) were significantly associated with lower risk of infection. Type of mask was not independently associated with infection. Those who wore masks all the time also were more likely to practice social distancing. Our findings suggest consistent wearing of masks, handwashing, and social distancing in public to protect against COVID-19 infection.
Associations between wearing masks, washing hands, and social distancing practices, and risk of COVID-19 infection in public: a cohort-based case-control study in Thailand