Fig. 1. Map of study site with study hospitals marked in blue. Sites of clusters of coronavirus disease outbreaks near the study hospitals are shown in red: ⓐ sports club, ⓑ call center, ⓒ church, ⓓ distribution center. The COVID-19 outbreak in a sport club (ⓐ) was detected on Jun 5, 2020, and visitors at the sport club from May 28 to June 2, 2020 were investigated. A call center (ⓑ) outbreak was first detected on March 9, 2020. Outbreak in a church (ⓒ) was detected on March 26, 2020 and outbreak at the distribution center (ⓓ) was detected on May 25, 2020.