1起社区水源性诺如病毒感染性腹泻暴发疫情的流行病学调查

目的探讨梅州市桌镇1起感染性腹泻暴发疫情的病因，提出针对性防控措施。方法按照病例定义开展病例搜索和个案调查，描述疾病的流行病学特征；调查患者饮食史，分析可能的暴露因素，并针对可疑因素开展回顾性队列研究；采集部分病例的粪便、肛拭子和呕吐物及自来水厂水源水、出厂水和管网末梢水、山泉水和井水等水样进行病原学及水质卫生学检测。结果2012年10月20日至28日，该镇共报告131例病例，罹患率为0．7％（131／18597）；首例发病时间为10月20日23时，高峰在10月21日至22日，占总数的80．2％（105／131）；病例主要表现以呕吐、腹泻；男、女性别比为0．7：1，以农民（38．9％）、学生（23．7％）和散居儿童（14．5％）为主；病例分布在该镇的13个村，发病数居前5位的村依次为A村30例（罹患率2．7％，30／1121）、B村24例（0．8％，24／2849）、C村21例（1．3％，21／1641）、D村18例（1．4％，18／1246）和E村10例（1．5％，10／692）。88．5％（116／131）的病例有采用集中式供水作为日常用水，使用自来水人群的8个村罹患率（1．0％，116／11135）较仅使用分散式供水人群（0．2％，15／7462）高，腹泻发病相对危险度（RR值）为5．2（95％CI：3．0～8．9），差异具有统计学意义。该镇共有3个自来水厂，其中供水范围最广的为x水厂，供应6个行政村（包括A、B、C、D、E和H村），人群罹惠率为1．3％（106／8166），Y水厂和Z水厂仅供应本村范围，其罹患率分别为0．4％（9／2149）和0．1％（1／820）。回顾性队列研究结果显示：与仅使用分散式供水人群比较，使用x水厂自来水是危险因素（RR=6．5，95％CI为3．8～11．1）。采集12份患者标本以及15份水样检测显示：8份患者标本（2份粪便标本、5份肛拭予和1份呕吐物）为诺如病毒核酸阳性；8份x水厂水样（包括1份水源水、2份出厂水和5份管网末梢水）的总大肠茵群和耐热大肠菌群超标；7份x水厂水样（包括1份出厂水、3份管网末梢水和3份水源水）和1份井水诺如病毒核酸检测阴性。结论该起疫情可能为水源性诺如病毒感染性腹泻暴发疫情。建议全市相关部门加强对农村集中式供水的监测与监管，确保饮用水安全。

Outbreak of waterborne infectious diarrhea associated with Norovirus in community

Objective To investigate the cause of an outbreak of infectious diarrhea in a town of Meizhou City and propose countermeasures for control of the outbreak. Methods We screened the cases according to the case definition, described the epidemiological characteristics, investigated the habits of drinking water and eating meals, and analyzed the possible exposure factors by carrying out retrospective cohort study. Then we collected clinical specimens, including stool specimens, rectal swabs, and vomitus of part patients, and water samples from waterworks including source water, finished water and tap water, mountain spring, and wells for microbiological and etiological detection. Results From October 20 to 28 in 2012, a total of 131 patients with infectious diarrhea were found in the town, with an attack rate of 0. 7% （ 131/18 597）. The initial case occurred at 23：00 pm on October 20, and the peak occurred from October 21 to 22, accounting for 80. 2% （ 105/131 ） of total cases. The main clinical symptoms were vomi-ting and diarrhea. The gender ratio was 0. 7： 1, and the main occupations were farmers （38. 9% ）, students （23.7%）, and scattered children （14. 5% ）. 13 villages were involved, and the top five villages in incidence were A （30 cases, attack rate 2.7% ）, B （24, 0. 8% ）, C （21, 1.3% ）, D （ 18, 1.4% ）, and E （ 10, 1.5% ）. 88.5% （ 116/131 ） cases used centralized water supply. The attack rate in eight vil- lages with centralized water supply （1.0%, 116/11 135 ） was higher than that in villages only using de- centralized water supply （0. 2%, 15/7 462）, and the relative risk （RR） was 5.2 （95% CI： 3.0 -8. 9）. There were three waterworks in the town. The X waterworks provided water supply for 6 villages of A, B, C, D, E, and H, where the attack rate was 1.3% （ 106/8 166）. Y and Z waterworks only supplied their own villages, where the attack rates were 0. 4% （9/2 149） and 0. 1% （ 1/820）, respectively. The results of retrospective cohort study indicated that using water from the X waterworks was a risk factor （RR = 6. 5, 95% CI： 3.8 - 11.1 ）. A total of 12 clinical specimens and 15 water samples were tested. 8 clinical speci- mens, including 2 stool specimens, 5 rectal swabs, and 1 vomitus were positive for Norovirus nucleic acid, 8 water samples from X waterworks, including 1 source water,2 finished water and 5 tap water from pipe network were positive for total coliform group and thermotolerant coliform bacteria, and 7 water samples from X waterworks, including 1 finished water, 3 tap water from pipe network and 3 source water, and 1 well water were negative for Norovirus nucleic acid. Conclusion The outbreak of infectious diarrhea oc- curred in a town of Meizhou City was waterborne and may be caused by Norovirus. We suggest that the rele- vant departments strengthen monitoring and supervision of centralized water supply in rural areas to ensure the drinking water safety.