The Association between Wearing a Mask and COVID-19.

With the widespread and increasing number of cases of Coronavirus Disease (2019) globally, countries have been taking preventive measures against this pandemic. However, there is no universal agreement across cultures on whether wearing face masks are an effective physical intervention against disease transmission. We investigated the relationship between mask wearing and COVID-19 among close contacts of COVID-19 patients in the Hiroshima Prefecture, Japan. In the Hiroshima Prefecture, a COVID-19 form adapted from the reporting form, "Japanese Surveillance in Post-Extreme Emergencies and Disasters", was developed to collect data from COVID-19 patients' close contacts under active epidemiological surveillance at Public Health Centers. The relative risk of COVID-19 for mask users versus non-mask users was calculated. A total of 820 interviewees were included in the analysis and 53.3% of them responded that they wore masks. Non-mask users were infected at a rate of 16.4%, while mask users were infected at a rate of 7.1%. Those who wore masks were infected at a rate of 0.4 times that of those who did not wear masks. (RR = 0.4, 95%CI = 0.3-0.6; Adjusted RR = 0.6, 95%CI = 0.3-0.9). These findings implied that COVID-19 could be avoided to a certain degree by wearing a mask.