一起中学GI.P2-GI.2型诺如病毒暴发疫情调查及厨工感染因素分析

Study on an outbreak caused by Norovirus GI.P2-GI.2 among kitchen workers in a secondary school and analysis on infection factors

目的 调查深圳市某中学一起诺如病毒感染暴发疫情,探索可能的传播途径和危险因素,为制定防控措施提供科学依据。方法 采用现场流行病学调查方法对病例进行个案调查,描述疾病流行特征,开展现场卫生学调查,采用病例对照研究探索厨工感染危险因素。采集病例和厨工肛拭子标本,用实时荧光定量PCR法检测诺如病毒核酸,部分阳性样本进行基因测序和系统进化分析。结果 2020年9月11—27日,深圳市某中学共发现学生病例31例,均为高三学生,罹患率为3.33%(31/930),无班级和宿舍聚集性,厨工26例检测诺如病毒阳性,其中2例发病,感染率为41.94%(26/62);厕所相邻班级的发病风险高于其余班级(OR=4.014,95%CI:2.012~8.009);每天使用食堂更衣室≥3次为厨工感染的危险因素(OR=7.378,95%CI:1.013~53.711)。104份肛拭子标本,经检测48份为GI型诺如病毒核酸阳性,厨工和学生病例的病毒测序结果为GI.P2-GI.2型,序列相似度为100.00%。88.46%(23/26)的感染厨工排毒时间超过10 d。结论 本次疫情为一起GI.P2-GI.2型诺如病毒感染暴发疫情,厨工可能经接触传播感染发病或隐性携带病毒,后污染食堂加工食品或餐具而传播给用餐学生。

Objective To explore the possible routes of transmission and risk factors and to provide scientific basis for the prevention and control measures by investigating an Norovirus infection outbreak in a secondary school of Shenzhen.Methods The case study and description of epidemic characteristics was conducted by field epidemiological investigation, and the hygiene survey was implemented, and a case-control study was employed to explore the risk factors related to kitchen workers.Anal swabs specimens from the patients and kitchen workers were collected, the Norovirus nucleic acid was tested by real-time fluorescence PCR,and some positive samples were further sequenced for phylogenetic analysis.Results A total of 31 student cases from a secondary school at Grade Ⅲ with the attack rate of 3.33%(31/930) were identified between September 11 and 27,2020.No clustering was found in different classes and dormitories, 26 kitchen workers were positive in Norovirus tests, 2 symptomatic cases with the infection rate of 41.94%(26/62) were found.The risk of morbidity in classes near the toilets was higher than that in other sites(OR=4.014,95%CI:2.012-8.009).The use of the canteen dressing room≥3 times daily was found to be a risk factor for kitchen workers′ infections(OR=7.378,95%CI:1.013-53.711).Totally 48 out of 104 anal swab specimens collected were positive in nucleic acid assays for GI-typed Norovirus.The viral sequencing results of kitchen workers and students cases showed genotype GI.P2-GI.2,and the sequences were 100.00% identical.The duration of Norovirus shedding from 88.46%(23/26) infected kitchen workers was greater than 10 days.Conclusion The epidemic is the outbreak of infectious diarrhea caused by Norovirus GI.P2-GI.2.Kitchen workers may be infected and attacked or recessively carry viruses through contact transmission, and then spread the disease to dining students by contaminating canteen processed food or tableware.