成都市首起新型冠状病毒奥密克戎变异株引起的本土聚集性疫情分析

Epidemiological characteristics of the first local Omicron variant COVID-19 outbreak in Chengdu

目的 分析成都市首起新型冠状病毒(SARS-CoV-2)奥密克戎变异株引起的本土疫情的流行病学特征,为疫情防控提供参考依据。方法 收集2022年2月20日—3月2日报告的新型冠状病毒肺炎(corona virus disease 2019,COVID-19)本土病例个案信息,采用WPS 2019软件管理数据,R 4.0.3软件进行数据分析和作图。结果 基因序列分析发现,本次疫情由奥密克戎变异株(BA.2进化分支)引起,疫情波及成都市3个区,病例以18~30岁的公司职员居多,男女性别比例为0.65∶1。37例续发病例均可追溯到指示病例的密接或次密,续发病例主要通过密切接触者筛查(32例,86.49%)发现,在家庭中接触(40.54%),以共同生活(35.14%)的方式暴露,所有病例均处于同一传播链。指示病例于2月20日报告,2月21日前,发病数呈快速增长,流行病学增长率r为0.26,病例数实现倍增的时间为2.70 d。病例的潜伏期和序列间隔分布在0~6 d,平均潜伏期和序列间隔分别为2.91 d和3.03 d。实时再生数Rt值在2月17日最高(7.61),目的基因(ORF1ab、N基因)Ct的中位数分别为22.72和19.56。所有病例均接种过COVID-19疫苗,37例完成全程接种。病例分类中,阳性检测占39.47%,确诊病例的临床分型均为轻型(23例,60.53%),症状以咽痛/咽痒、咳嗽、发热多见。结论 奥密克戎变异株的序列间隔和潜伏期短,传染性强,易突破现有疫苗建立的免疫屏障,但病例症状均较轻。

Objective To analyze the epidemiological characteristics of the first local Omicron variant COVID-19 outbreak in Chengdu and to provide evidence for the prevention and control of COVID-19. Methods The epidemiological data of local COVID-19 cases were retrospectively collected from field investigation during February 20 and March 2, 2022.Software WPS 2019 was used for data management and software R 4.0.3 was used for statistical analysis and graphing. Results Gene sequencing analysis showed that the outbreak was caused by SARS-COV-2 Omicron variant(BA.2 evolutionary branch), and 3 districts in Chengdu were involved.Majority of cases were company employees aged 18-30 years, and male-to-female ratio was 0.65∶1. All patients were in the same transmission chain, and 37 secondary cases could be traced as close contacts or sub-close contacts of the index case.Majority of secondary cases were detected by close contacts screening(32 cases, 86.49%).Living together(35.14%) and family exposure(40.54%) were the leading paths of infection.The index case was reported on February 20, and the number of cases increased rapidly before February 21.The epidemiological growth rate r was 0.26, and the cases doubledi n only 2.70 d.Thei ncubation periodand serial interval ranged from 0 to 6 days, with the average of 2.91 d and 3.03 d.The time dependent repr oduction number Rt peaked on February 17(7.61), and median value of Ct was 22.72 for ORF1ab gene and 19.56 for N gene.All cases had been vaccinated, and 37 were fully vaccinated.Most cases were classified asconfirmed cases, and 23(60.53%) were mild cases.Sore throat, cough and fever were the most common symptoms. Conclusions Omicron variant has short incubation period and serial interval with strong infectivity, which can break through the immune barrier established by existing vaccines, however the symptoms of casesare usually mild.