Epidemiological characteristics of a COVID-19 outbreak caused by religious activities in Daegu, Korea

OBJECTIVES: A coronavirus disease 2019 (COVID-19) outbreak triggered by religious activities occurred in Daegu, Korea in February 2020. This outbreak spread rapidly to the community through high-risk groups. This study describes the characteristics of COVID-19 cases based on S religious group membership and summarizes the Daegu municipal government’s processes and responses to control the outbreak. METHODS: The epidemiological characteristics of confirmed cases were obtained through basic and in-depth epidemiological surveys. General characteristics, the proportion of asymptomatic cases, the case-fatality rate, and the time-to-event within each group were presented after stratifying confirmed cases according to S religious group membership. RESULTS: Overall, 7,008 COVID-19 cases were confirmed in Daegu from February 18, 2020 to June 30, 2020, and 61.5% (n=4,309) were S religious group members. Compared with non-members, members had a higher proportion of female (p<0.001) and younger age (p<0.001), as well as lower disease prevalence. At the time of the investigation, 38.4% of cases in members were asymptomatic versus 23.7% of cases in non-members (p<0.001). The case-fatality rate of non-members aged ≥ 60 years was significantly higher than that of members (p<0.001). Compared with non-members, members had longer intervals from symptom onset to diagnosis (p<0.001) and from diagnosis to admission (p<0.001), and a shorter interval from admission to discharge (p<0.001). CONCLUSIONS: The epidemiological features of S religious group members, including the proportion of asymptomatic cases, case-fatality rate, and time-to-event, differed from non-members. The Daegu authorities prevented further COVID-19 spread through immediate isolation and active screening tests of all S religious group members.