Associations between mask-wearing, handwashing, and social distancing practices and risk of COVID-19 infection in public: a case-control study in Thailand

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 ≤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. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The study was supported by the Department of Disease Control (DDC), Ministry of PUblic Health (MoPH) Thailand. DL is supported by the Wellcome Trust (106698/Z/14/Z). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: As this study was part of the routine situation analysis and outbreak investigation of the DDC MoPH Thailand, it was not required to obtain ethics approval and no written informed consent was collected. However, the study team strictly followed ethical standards in research, that is, all individual information was strictly kept confidential and not reported in the paper. The DDC MoPH Thailand approved the analysis and reporting of data in aggregate. All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data in aggregate are reported in the manuscript.