Field Epidemiology Training Program, National Institute of Infectious Diseases, Japan.
Antimicrobial Resistance Research Center, National Institute of Infectious Diseases, Japan.
Jpn J Infect Dis. 2022 Mar 24;75(2):192-194. doi: 10.7883/yoken.JJID.2021.230. Epub 2021 Aug 31.
An outbreak of coronavirus 2019 (COVID-19) occurred in Ueda City, Nagano prefecture, Japan, which has a population of 150,000. The residents were a population naïve to COVID-19, and many of them had only one chance of exposure, in which careful epidemiological investigation could reveal attack rates among close contact on the specific date of exposure. We identified 89 cases and 328 close contacts. Among the close contacts, 114 had only one chance of exposure to the 20 index cases. During the follow-up period, 17 close contacts tested positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), overall attack rate of 15%, after the exposure to 6 infectors. The median number of close contacts for the 6 infectors was 5.5 (range 2-14). Attack rates among these close contacts were 13% (1/8), 20% (2/5), 33% (2/6), 50% (1/2), 64% (4/9 and 5/5), and 100% (2/2), respectively. The transmission risk of SARS-CoV-2 appears to peak one day before symptom onset, and is at similar levels two days before (16%) and on the day (20%) of symptom onset. A multidisciplinary approach is needed to control the COVID-19 outbreak, in addition to investigation, which began after case identification.
日本长野县上田市发生了 2019 年冠状病毒病（COVID-19）疫情，该市人口为 15 万。居民对 COVID-19 没有免疫力，他们中的许多人只有一次接触的机会，在这种情况下，仔细的流行病学调查可以揭示在特定接触日期与密切接触者的发病情况。我们共确定了 89 例病例和 328 名密切接触者。在这些密切接触者中，有 114 人只有一次机会接触到 20 名索引病例。在随访期间，17 名密切接触者的严重急性呼吸系统综合征冠状病毒 2（SARS-CoV-2）检测呈阳性，暴露于 6 名感染者后，总发病率为 15%。6 名感染者的密切接触者中位数为 5.5（范围 2-14）。这些密切接触者的发病率分别为 13%（1/8）、20%（2/5）、33%（2/6）、50%（1/2）、64%（4/9 和 5/5）和 100%（2/2）。SARS-CoV-2 的传播风险似乎在症状出现前一天达到高峰，在症状出现前两天（16%）和当天（20%）的水平相似。除了在病例确定后开始的调查外，还需要采取多学科方法来控制 COVID-19 疫情。
