Epidemiological characteristics of a local COVID-19 outbreak caused by Omicron (BA.2.2) variant in Henan province
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摘要:
目的 分析河南省一起外省输入病例引发本地新冠肺炎聚集性疫情的调查过程、疫情特点和传播过程。 方法 将2022年3月18 — 28日河南省焦作市修武县的新冠肺炎本土疫情感染者作为研究对象，收集其流行病学调查、实验室检测、临床表现等信息，采用描述流行病学方法进行分析。 结果 按照报告日期疫情持续11 d，共报告45例感染者；男性16例，女性29例；年龄中位数M（P25，P75）为43岁（27.5，58.0）；无症状感染者31例，确诊病例14例（轻型13例、普通型1例），无重症和死亡病例；初筛阳性Orf1ab基因CT值中位数M（P25，P75）为23.02（18.57，28.64），N基因CT值中位数M（P25，P75）为23.10（18.63，28.03）；出现1起纺织工厂较大聚集性疫情，工厂罹患率为6.6 %；涉及7起家庭聚集性疫情，家庭续发率为20.78 %，密接续发率为3.79 %；12.5 %的感染者暴露于既未出现临床症状核酸检测又阴性时的感染者；疫情传染源为从上海返乡人员，病毒基因测序为奥密克戎变异株BA.2.2，潜伏期中位数M（P25，P75）为3 d（2，4.25）；代间距中位数M（P25，P75）为3 d（2，3），共发生5代病例。本次疫情的R0为6.14，实时再生数Rt于采取防控措施后2 d出现下降，在采取措施后8 d降至1以下。 结论 河南省本起疫情为外省输入引起，主要通过工厂、家庭、学校传播，控制措施较好，未造成外溢，重点人群核酸筛查对早期发现疫情具有重要意义。 -
关键词:
- 新冠肺炎 /
- 奥密克戎变异株BA.2.2 /
- 流行特征
Abstract:Objective To analyze epidemiological characteristic and transmission process of a local coronavirus disease 2019 (COVID-19) outbreak induced by imported cases from other provinces in Henan province. Methods The data on all local COVID-19 cases in Xiuwu county, Henan province reported during March 18 – 28, 2022 were extracted from National Notifiable Disease Report System. The results of field investigations on the cases were also collected simultaneously. Descriptive statistics was performed on the data collected with SPSS 22.0. Results Totally 45 cases (16 males and 29 females, 14 minor or common patients and 31 asymptomatic infections) were reported during the 11-day outbreak period. The median age (25th percentile [P25], 75 percentile [P75]) of the cases was 23.02 (18.57, 28.64) years. The median (P25, P75) of cycle threshold (Ct) value for Orf1ab gene and N gene for positive cases in primary screening were 23.02 (18.57, 28.64) and 23.10 (18.63, 28.03), respectively. A case clustering involving 18 cases was identified in a local textile factory, with an incidence rate of 6.6%; seven family clusters were also identified, with a family secondary attack rate of 20.78% and a secondary attack rate of 3.79% among close contacts. Of all the cases, 12.5% could attributed the infection to the exposure to the asymptomatic infections being negative for nucleic acid test at that time. The results of genome second generation sequencing for the isolates from 29 infections indicated that the pathogen of the outbreak was severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant Omicron (BA.2.2) and the local transmission of the virus variant was traced back to the 2 first generation cases returning home from other epidemic area. The median (P25, P75) of incubation period was 3 (2, 4.25) days and that of generation interval was 3 (2, 3) days. Five generations of transmission were identified for the outbreak . The estimated basic reproductive number (R0) of this epidemic was 6.14, and the effective reproduction number (Rt) decreased 2 days after the control measures were taken and declined to less than 1 in 8 days after the implementa-tion of control measures. Conclusion The reported COVID-19 outbreak in Henan province was caused by imported cases from other epidemic area and spread mainly in factories, families and schools. The control measures on the outbreak were effective and subsequent transmission was prevented. -
Key words:
- COVID-19 /
- Omicron (BA. 2.2) variant /
- epidemiological characteristics
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图 1 45例感染者传播链示意图
注：5号为首发病例，1号和2号为指示病例，3号和4号为传染来源；1～5、8、9、11～16、19～23、25～18、30、31、36～39号完成了病毒基因测序，37号变异位点为73 + C14120T，39号变异位点为73+C28256T，其余均为73个。
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