Public health interventions have served an important role in controlling coronavirus disease 2019 (COVID-19), a rapidly spreading infectious disease. To contribute to future COVID-19 countermeasures, we aimed at verifying the results of countermeasures achieved by public health centers (PHCs) against the first wave of COVID-19 in Yamagata Prefecture, Japan. During January–May 2020, 1,253 patients suspected of SARS-CoV-2 infection were invited for testing. Simultaneously, based on retrospective contact tracings, PHCs investigated the infection sources and transmission routes of laboratory-confirmed COVID-19 cases and tested 928 contacts. Consequently, 69 cases were confirmed during March 31 – May 4, 58 (84.1%; 95% confidence interval 75.5–92.7) of whom were found from contacts. The spread of infection was triggered by cases harboring epidemiological links outside of Yamagata. Then, the number of cases increased rapidly. However, PHCs identified epidemiological links in 61 (88.4%; 95% confidence interval 80.8–96.0) of the 69 cases and transmission chains up to the fifth generation. Finally, the spread of infection ended after approximately one month. Our results indicate that the identification of infection sources and active case finding from contacts based on retrospective contact tracing was likely to be an effective strategy to end the first wave of COVID-19 in Yamagata.

公共卫生干预措施在控制 2019 年冠状病毒病 (COVID-19) 方面发挥了重要作用，这是一种迅速传播的传染病。为了为未来的 COVID-19 对策做出贡献，我们旨在验证公共卫生中心 (PHC) 针对日本山形县第一波 COVID-19 所采取的对策的结果。2020 年 1 月至 5 月期间，邀请了 1,253 名疑似感染 SARS-CoV-2 的患者进行检测。同时，基于回顾性接触者追踪，PHC 调查了实验室确诊的 COVID-19 病例的感染源和传播途径，并测试了 928 名接触者。因此，在 3 月 31 日至 5 月 4 日期间确认了 69 例病例，其中 58 例（84.1%；95% 置信区间 75.5-92.7）来自接触者。感染的传播是由与山形县以外的流行病学联系的病例引发的。随后，病例数迅速增加。然而，初级卫生保健人员在 69 例病例中的 61 例（88.4%；95% 置信区间 80.8-96.0）和直至第五代的传播链中确定了流行病学联系。最后，感染的传播在大约一个月后结束。我们的结果表明，基于回顾性接触者追踪从接触者中识别感染源和活跃病例可能是结束山形县第一波 COVID-19 浪潮的有效策略。感染的传播在大约一个月后结束。我们的结果表明，基于回顾性接触者追踪从接触者中识别感染源和活跃病例可能是结束山形县第一波 COVID-19 浪潮的有效策略。感染的传播在大约一个月后结束。我们的结果表明，基于回顾性接触者追踪从接触者中识别感染源和活跃病例可能是结束山形县第一波 COVID-19 浪潮的有效策略。