Types of COVID-19 clusters and their relationship with social distancing in Seoul Metropolitan area in South Korea

Choi, Yoon-Jung; Park, Mi-jeong; Park, Soo Jin; Hong, Dongui; Lee, Sohyae; Lee, Kyung-Shin; Moon, Sungji; Cho, Jinwoo; Jang, Yoonyoung; Lee, Dongwook; Shin, Aesun; Hong, Yun-Chul; Lee, Jong-Koo

Background Complete contact tracing of COVID-19 patients in Korea allows a unique opportunity to investigate cluster characteristics. This study aimed to investigate all the reported COVID-19 clusters in Seoul Metropolitan area from January 23 to September 24, 2020. Methods Publicly available COVID-19 data was collected from the Seoul Metropolitan city and Gyeonggi Province. Community clusters with ≥ 5 cases were characterized by size and duration and then categorized using K-means clustering, and the correlation between the types of clusters and the level of social distancing was investigated. Results A total of 134 clusters including 4,033 cases were identified. The clusters were categorized into small (Type I, II), medium (type III), and large (type IV) clusters. With the same number of daily confirmed cases, cases were composed of different types of clusters by different periods of time. Raising social distancing was related with shifting types of clusters from large to small sized clusters. Conclusions Classification of clusters may provide opportunities to better portray the pattern of COVID-19 outbreaks and implement more effective strategies. Social distancing administered by the government may be effective in suppressing large clusters but may not be effective in controlling small and sporadic clusters.