[Analysis on the household secondary attack rates of the SARS-CoV-2 Delta variant and the associated factors].

Objective: To evaluate the household secondary attack rates of the SARS-CoV-2 Delta variant and the associated factors. Methods: A COVID-19 outbreak caused by the Delta variant occurred in Nanjing in July 2021. A total of 235 cases with current addresses in Nanjing were reported from 171 households. The subjects in this study were selected from household close contact(s) of infected cases. The information on household index cases and their contacts were collected, and the household secondary attack rate (HSAR) and the risk factors were analyzed by the multi-factor logistic regression model. Results: A total of 234 cases of household close contacts and 64 household secondary cases were reported from 103 households, and the HSAR was 27.4% (64/234, 95%CI:22.0% to 33.4%). The proportions of household size for 2 to 3, 4 to 5, and 6 to 9 were 64.1% (66), 26.2% (27) and 9.7% (10), respectively. A total of 35 cases of household cluster outbreaks were reported (35/103, 34.0%). The number of the first case in the household (FCH) was 103 and males accounted for 27.2% (28 cases), with the median age (Q1, Q3) of 49 (9, 56). The number of household close contacts was 234 and males accounted for 59.0% (138 cases), with the median age (Q1, Q3) of 42 (20, 55) and the median exposure period (Q1, Q3) of 3 (1, 3) days. The multi-factor logistic regression model showed that the higher HSAR was observed in the FCH with the features of airport staff (OR=2.913, 95%CI:1.469-5.774), detection from home quarantine screening (OR=6.795, 95%CI:1.761-26.219) and detection from mass screening (OR=4.239, 95%CI:1.098-16.368). Meanwhile, higher HSAR was observed in cases with longer household exposure (OR=1.221, 95%CI:1.040-1.432), non-vaccination (OR=2.963, 95%CI:1.288-6.813) and incomplete vaccinations (OR=2.842, 95%CI:0.925-8.731). Conclusion: The generation interval of the Delta variant is shortened, and the ability of transmission within the household is enhanced. In the outbreak in Nanjing, the associated factors of HSAR are occupation, detection route, vaccination and exposure period.目的： 分析新型冠状病毒Delta变异株引起的家庭二代续发率（HSAR）及影响因素。 方法： 2021年7月南京市报告一起Delta变异株引起的聚集性疫情，累计报告现住址为南京市的病例235例，分布于171个家庭，筛选出存在家庭密接接触者（家庭密接）的家庭及家庭密接作为研究对象，收集家庭首发病例和家庭密接相关信息，采用多因素logistic回归模型分析家庭HSAR及影响因素。 结果： 103个家庭共报告家庭密接234名、家庭续发病例64例，HSAR为27.4%（95%CI：22.0%~33.4%），家庭规模2~3、4~5、6~9人的家庭分别占64.1%（66个）、26.2%（27个）、9.7%（10个）；共报告家庭聚集性疫情35起，占34.0%（35/103）。103例家庭首发病例中，男性占27.2%（28例），年龄M（Q1，Q3）为49（9，56）岁；234名家庭密接中，男性占59.0%（138例）；年龄M（Q1，Q3）为42（20，55）岁；暴露时间M（Q1，Q3）为3（1，3）d。多因素logistic回归模型分析结果显示，家庭首发病例为机场工作人员（OR=2.913，95%CI：1.469~5.774）、发现途径为居家隔离筛查（OR=6.795，95%CI：1.761~26.219）和社会面筛查（OR=4.239，95%CI：1.098~16.368）的家庭内HSAR风险更高；家庭密接暴露时长越长（OR=1.221，95%CI：1.040~1.432）、未接种疫苗（OR=2.963，95%CI：1.288~6.813）和未全程接种疫苗（OR=2.842，95%CI：0.925~8.731）的家庭内HSAR风险更高。 结论： Delta变异株代间距缩短，家庭内传播能力较强；家庭首发病例是否为机场工作人员、发现途径，以及家庭密接疫苗接种、暴露时长是家庭HSAR的影响因素。.