[Epidemiological characteristics of a local cluster epidemic caused by 2019-nCoV Delta variant in Ningbo, 2021].

Objective: To understand the epidemiological characteristics of a local clustered epidemic caused by 2019-nCoV Delta variant in Ningbo and provide reference for the improvement of COVID-19 epidemic prevention and control. Methods: Case finding was conducted based on case definitions, and field epidemiological investigation of COVID-19 cases was carried out. In which Nasal and oropharyngeal swabs of the cases were collected for pathogen testing, and the results were analyzed with descriptive epidemiological methods. Results: A total of 74 COVID-19 cases were reported in this epidemic, and the cases were mainly mild ones, accounting for 87.84% (65/74), and there were no severe or critical cases. The epidemic curve showed a human-to-human transmission mode, indicating that a transmission for at least six generations had occurred. The age of the COVID-19 patients ranged from 2 years to 80 years, and 27.03% (20/74) of the cases were older than 60 years. The cases were mainly workers (55.41%, 41/74) and housework/the unemployed (27.03%, 20/74). The COVID-19 epidemic was limited, and no further spread to other areas occurred. The transmission chain among the cases was clear, and the gene sequencing results confirmed that the current epidemic was caused by 2019-nCoV Delta variant, which was highly homologous to the strains from other province. Conclusion: The local COVID-19 epidemic in Ningbo was caused by imported cases of COVID-19 from other province, and local community spread occurred through daily contacts between cases and contacts.目的： 分析宁波市一起新型冠状（新冠）病毒Delta变异株本土聚集性疫情流行特征，为完善新型冠状病毒肺炎（COVID-19）疫情防控政策提供参考依据。 方法： 通过制定病例定义，开展病例搜索，对发现的病例开展现场流行病学调查，采集相关标本开展病原学检测，运用描述流行病学方法进行分析。 结果： 本起疫情累计报告74例确诊病例，病例以轻型为主，占87.84%（65/74），无重型和危重型。流行曲线呈人传人传播模式，据流行病学调查显示，本起疫情至少传播6代。病例年龄范围为2~80岁，其中≥60岁占27.03%（20/74）。职业分布中以工人占55.41%（41/74）和家务/待业占27.03%（20/74）为主，疫情局限，未发生病例外溢。病例间流行病学关联明确，传播链清晰。基因测序结果证实为新冠病毒Delta变异株，与浙江省外输入关联疫情高度同源。 结论： 本起疫情为一起浙江省外输入COVID-19确诊病例引起的本土聚集性疫情，通过生活、工作接触导致社区传播扩散。.