1起肠聚集性大肠埃希菌引起的学生群体性腹泻事件调查

Investigation of a diarrhea outbreak induced by enteroaggregative E.coli in students

目的对1起高中生群体性腹泻事件进行调查,查找病原和事件发生原因,为预防学校类似事件提供依据。方法制定病例定义,开展病例搜索和个案问卷调查,描述流行特征。通过病例对照研究,分析危险餐次和食物。开展现场卫生学调查,采集肛拭子和食物原料、加工环节涂抹标本,采用聚合酶链反应(Polymerase Chain Reaction,PCR)检测病原。结果此次事件只涉及该校住宿班学生,共有116名学生发病,涉及在住宿生餐厅就餐的所有班级,住宿班学生总体罹患率为20.32%(116/571)。男、女生罹患率分别为30.20%(61/202)、14.91%(55/369),差异有统计学意义(RR=2.03,95%CI:1.47~2.79)。病例对照研究显示,暴露于5月30日晚餐为危险因素(OR=3.49;95%CI:1.81~6.74),可疑食物为凉拌菜椒麻鸡(OR=4.83;95%CI:2.51~9.28),椒麻鸡进食量与发病有相关性(线性趋势χ~2=22.37,P<0.01)。11名发病学生肛拭标本中,7份检出肠聚集性大肠埃希菌ast A毒力基因。住宿生餐厅的食物原料鸡胸肉以及加工菜肴的菜板、刀具、菜盆等环境涂抹标本中亦检出ast A毒力基因。该学校餐厅存在违规制售凉拌菜、食物加工过程中存在交叉污染等问题。结论此次事件是1起由肠聚集性大肠埃希菌引起的学生群体性腹泻事件,交叉污染是此次事件发生的重要原因。学校食堂应加强食品卫生管理,杜绝供应凉拌菜,生熟分开,避免交叉污染。

[Objective]To find the pathogen and risk factors of a diarrhea outbreak in high-school students and provide basis for prevention of similar event in schools. [Methods] Case definitions were developed for case searching and case questionnaire survey, to describe the epidemiological characteristics. A case-control study was conducted to explore the risk factors including meals and food. Field hygiene investigation was carried out, while anal swabs, food materials and environment smear specimens were collected for detection of pathogens through polymerase chain reaction（PCR）.[Results] 116 cases occurred in the outbreak involving all 4 grades of boarders dining in the residential restaurant. The overall attack rate was 20.32%（116/571）. The attack rate of boys and girls were 30.20%（61/202）, 14.91%（55/369） respectively with a statistically significant difference（RR=2.03,95%CI： 1.47-2.79）. Case-control study showed that exposure to the dinner of May 30 was a risk factor（OR=3.49; 95%CI： 1.81-6.74） and the suspicious food was the cold dish of pepper chicken（OR=4.83; 95%CI： 2.51-9.28）. Intake of the pepper chicken was statistically correlated with morbidity（linear trend χ~2=22.37, P〈0.01）. 7 of 11 anal swabs from cases were positive of heatstable enterotoxin gene（ast A） of Enteroaggregative Escherichia coli（EAEC）. The enterotoxin gene was also found in the food material of chicken breast, cutting board, kitchen knife and food pots. Such matters existed in the residential restaurant,including illegal supply of cold dishes, cross-contamination in the process of making food. [Conclusion] The diarrhea outbreak is induced by EAEC. Cross-contamination is the most important reason for the occurrence of this event. School restaurant should strengthen food hygiene management, prevent the supply of cold dishes and pay attention to separation of raw and cooked food to avoid cross-contamination.