Confirmation and epidemiological investigation of a GII.P7-GII.6 norovirus outbreak in a primary school of Jinshan District, Shanghai

Abstract

Objective To analyze the epidemiological characteristics of an acute gastroenteritis outbreak in a primary school caused by norovirus and the genotype of the pathogen, and we identify the mode of transmission for providing strategies for disease prevention and control.

Methods Cases were identified according to the definition, descriptive epidemiological approaches and retrospective case-control study designs were used for analysis. Stool or anal swab samples were collected from students and teachers by random sampling, anal swabs from the kitchen workers and environmental surface samples from the kitchen and classrooms were collected. The samples were detected by real-time PCR for norovirus, and polymerase region and capsid protein N/S region were amplified by PCR. The PCR products were purified, sequenced and compared with sequences stored in GenBank. The sequences aligned by MEGA 7.0 program package were used to construct the phylogenetic trees. The database was established by adopted Excel2017 software and was analyzed by OpenEpi software version 3.0.3 online.

Results A total of 44 acute gastroenteritis patients were reported in the school of Jinshan from 4th to 13th May, 2019, and the attack rate of 5.42%(44/812), with 41 students and 3 teachers. The main symptoms included vomiting(70.45%)and diarrhea (36.36%). The epidemic curve showed that homologous exposure followed by contacted transmission, the attack rate of Class Two Grade Five (38.46%) was much higher than that of other 9 classes. Results from the retrospective case-control study revealed that 3 days prior exposure to suspected patients ( RR= 6.43, 95% CI= 3.69-11.21), and exposing to vomit ( RR=5.26, 95% CI=3.20-8.65) would increase the risk of disease. Stools and anal swabs of 10 students and 3 teachers and one kitchen staff were found G II NoV positive when detected by real-timePCR. Seven stains of Jinshan|xingtaschool01|2019 and Jinshan|xingtaschool02|2019 belonged to the G II . P7-G II. 6 norovirus, which indicated virus homology.

Conclusion According to the epidemiological survey, clinical information and laboratory test, the outbreak of norovirus gastroenteritis was caused by G II. P7—G II. 6 norovirus, which caused by the recessive infection kitchen staff, contacting patients students and exposing to vomit led to the spread of the disease.

Abstract

摘要： 目的 分析一起学校诺如病毒感染性腹泻疫情流行病学特征及其感染病毒基因型别, 探讨可能传播途径, 为制定有效控制策略提供科学依据。 方法 制定统一病例定义, 开展主动病例搜索, 采用描述性流行病学和回顾性队 列研究进行分析；采集发病学生和老师粪便或肛拭子, 食堂员工肛拭子及食堂环境样本, 发病班级环境样本, 运用实时 荧光 RT-PCR 进行诺如病毒核酸检测, 应用常规 RT-PCR 扩增诺如病毒多聚酶区和衣壳蛋白 N/S 区, PCR产物纯化、测 序, 序列经核酸比对确认, 应用 MEGA 7.0 软件编辑基因序列, 构建系统进化树；采用Excel2017软件建立数据库, OpenEpi3.03 在线软件进行统计学分析。 结果 2019 年 5 月 4一13 日, 本起疫情报告病例 44 例, 罹患率为 5.42% (44/812), 学生 41 例, 教师 3 例;病例主要表现为呕吐 (70.45%), 腹泻 (36.36%) ；流行曲线提示同源暴露后继之以接触模式传播, 五(2)班罹患率 (38.46%) 高于其他 9 个班级;发病前 3 日接触类似病例 ( RR=6.43, 95% CI=3.69~11.21) 及近距离暴露呕 吐物 ( RR=5.26, 95% CI=3.20~8.65) 均为本起疫情危险因素。检测证实： 10 份学生、3 份老师及 1 份厨工粪便或肛拭子样 本 G II 型诺如病毒核酸阳性；随机测序样本序列比对:Jinshan|xingtaschool01|2019、Jinshan|xingtaschool02|2019等 7 株同 属 G II. P7-G II. 6 型诺如病毒, 指示病毒同源。 结论 结合流行病学调查、临床资料和实验室检测结果, 证实本次疫情 为由隐性感染厨工污染饭盒后继之以接触传播导致的 G II. P7-G II. 6 型诺如病毒感染性疫情。