Clusters of Coronavirus Disease in Communities, Japan, January-April 2020

Abstract

We analyzed 3,184 cases of coronavirus disease in Japan and identified 61 case-clusters in healthcare and other care facilities, restaurants and bars, workplaces, and music events. We also identified 22 probable primary case-patients for the clusters; most were 20-39 years of age and presymptomatic or asymptomatic at virus transmission.

Keywords: 2019 novel coronavirus disease; COVID-19; Japan; SARS; SARS-CoV-2; coronavirus; epidemiology; respiratory infections; severe acute respiratory syndrome coronavirus 2; transmission; viruses; zoonoses.

Figure 1

Analysis of 61 clusters of coronavirus disease (COVID-19) cases in communities in Japan, January 15–April 4, 2020. A) Cumulative number of COVID-19 cases, including the proportion of local cases with epidemiologic links to known confirmed cases. B) Distribution of clusters by number of cases in a cluster by category. C) Incidence of clusters of cases according to epidemiologic week as determined by date of confirmation of the first case in a cluster. Incidence of COVID-19 cases (weekly number of newly reported cases) in Japan and timing of two importation waves are also displayed. Epidemiologic week 3 corresponds to January 15, 2020, in panel A. The data and trend of imported cases were previously reported and described by Furuse et al. (8).

Figure 2

Analysis of probable primary cases of coronavirus disease (COVID-19) among 22 clusters in communities, Japan. A) Age ranges of probable primary COVID-19 cases in clusters. Age distribution among all COVID-19 cases in Japan is provided as reference. B) Proportions of symptoms among probable primary cases of COVID-19 clusters at transmission (n = 16) and among at laboratory confirmed diagnosis (n = 22). 1, Asymptomatic; 2, fever; 3, fatigue; 4, cough; 5, sore throat; 6, headache; 7, arthralgia or myalgia; 8, runny nose; 9, diarrhea; 10, difficulty breathing. C) Distribution of probable primary cases of COVID-19 clusters by time of transmission compared with illness onset by age groups (n = 16). Six cases were excluded because the time of transmission was undetermined.