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Familial Clusters of Coronavirus Disease in 10 Prefectures, Japan, February−May 2020

Year: 2021

Type: article

Abstract: A s of May 31, 2020, Japan had reported >16,800 confirmed coronavirus disease (COVID-19) cases and 890 related deaths.The cluster-based approach is one of the pillars of control measures in Japan (1).Sixty-one clusters were documented in healthcare facilities, restaurants, workplaces, and music venues during January-April 2020 (2).However, the transmission within households, one of the highest-risk settings, has not been fully investigated.A meta-analysis of 43 studies showed that the pooled household secondary attack rate (SAR) was 18.1%, and heterogeneity ranged from 3.9% to 54.9% (3).Heterogeneity of SAR could occur because of variations in susceptibility to infection (3), variations in exposure (4), and variations in infectiousness.The primary cases of infectiousness defined by age, sex, and symptoms were less studied in the different settings.Furthermore, there were few reports of SAR among asymptomatic primary cases (3,5,6).Therefore, we estimated the SAR of COVID-19 and assessed the effects of age and sex of primary cases, symptoms of primary cases, and the time between diagnosis and symptom onset for primary cases on infectiousness in familial clusters.The Study Among 47 prefectures in Japan, 10 prefectures (Aomori, Akita, Gunma, Tochigi, Toyama, Shiga, Okayama, Kochi, Saga, and Kagoshima) (Appendix Figure 1, https://wwwnc.cdc.gov/EID/article/27/3/20-3882-App1.pdf) that showed a relatively low COVID-19 prevalence posted laboratory-confirmed cases and contact-tracing results on their websites (Appendix Table 1).In this study, we collected basic characteristics of cases from the reports issued during February 22-May 31, 2020, on those websites.The websites did not provide characteristics of uninfected close contacts or details of residence of family members.During the study period in Japan, doctors provided diagnoses of COVID-19 by using real-time PCR and reported cases to healthcare centers.These centers listed close contacts according to whether they spent >15 min in faceto-face contact and conducted follow-up by telephone for >14 days to monitor their symptoms.Persons who had any COVID-19-related signs/ symptoms, such as fever, cough, and fatigue, were categorized as having symptomatic cases.Asymptomatic cases were those without any symptoms at diagnosis.During this study period, all confirmed case-patients were hospitalized after they were given a diagnosis.Suspected case-patients and asymptomatic close contacts self-quarantined at home.Healthcare centers in 8 prefectures performed PCRs for close contacts regardless of their symptoms.One prefecture did not show the strategy of PCR testing for asymptomatic contacts, and 1 prefecture performed PCRs for symptomatic contacts, such as persons who had fever and respiratory symptoms. Familial Clusters of Coronavirus Disease in 10 Prefectures, Japan,

Source: Emerging infectious diseases

DOI: 10.3201/eid2703.203882