Objective: To investigate a cluster epidemic of COVID-19 after a mass gathering activity in Ningbo of Zhejiang province and analyze the transmission chain and status of infection cases of different generations. Methods: The tracking of all the close contacts of the first COVID-19 case and epidemiological investigation were conducted on January 29, 2020 after a cluster epidemic of COVID-19 related with a Buddhism rally on January 19 (the 1.19 rally) in Ningbo occurred. The swabs of nose/throat of the cases and close contacts were collected and tested for nucleic acids by real-time fluorescence quantitative RT-PCR. Results: From January 26 to February 20, 2020, a total of 67 COVID-19 cases and 15 asymptomatic infection cases related with the 1.19 rally were reported in Ningbo. The initial case was the infection source who infected 29 second generation cases and 4 asymptomatic infection cases, in whom 23 second generation cases and 3 asymptomatic infection cases once took bus with the initial case, the attack rate was 33.82% (23/68) and the infection rate was 38.24% (26/68). The risks of suffering from COVID-19 and being infected were 28.91 times and 26.01 times higher in rally participants taking bus with initial case compared with those taking no bus with initial case. In this epidemic, 37 third+generation cases and 11 related asymptomatic infection cases occurred, the attack rate was 2.88% (37/1 283) and the infection rate was 4.76% (48/1 008). The main transmission routes included vehicle sharing and family transmission. Conclusion: It was a cluster epidemic of COVID-19 caused by a super spreader in a massive rally. The epidemic has been under effective control.
目的： 调查宁波市大型集会活动引起的一起新型冠状病毒肺炎聚集性疫情，分析其引发的传播链和各代病例感染情况。 方法： 针对宁波市2020年1月19日大型佛教集会活动（1.19活动）引起的一起新型冠状病毒肺炎聚集性疫情的首发病例，1月29日开展所有感染病例的密切接触者的追踪和筛查，完成流行病学个案调查，采集其鼻/咽拭子标本采用实时荧光定量RT-PCR法进行新型冠状病毒核酸检测。 结果： 宁波市2020年1月26日至2月20日报告确诊病例67例和无症状感染者15例，与1.19活动相关。首发病例为本次聚集性疫情的传染源，其二代病例29例，无症状感染者4例，其中，首发病例和确诊病例23例及无症状感染者3例的密切接触史为共同乘坐旅游巴士，罹患率为33.82%（23/68），感染率为38.24%（26/68），与首发病例同车人员的发病风险和感染风险分别是活动其他参与者的28.91倍和26.01倍。本次疫情三代及以上确诊病例37例、无症状感染者11例，罹患率为2.88%（37/1 283），感染率为4.76%（48/1 008）。主要的传播方式为同车密切接触和家庭内传播。 结论： 这是一起大型集会活动为起因的超级传播者引发的聚集性疫情事件，该疫情已得到有效控制。.
Keywords: COVID-19; Close contact; Cluster.