金山区某学校一起诺如病毒感染性腹泻疫情流行病学调查

Epidemiological investigation on an outbreak of norovirus-induced infectious diarrhea in a primary school in Jinshan Dstrict

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,为有效控制疫情提供科学依据,同时为类似疫情现场处置提供经验。方法制定统一病例定义,在全校学生及教职员工中开展主动病例搜索,采用描述性流行病学和回顾性队列研究进行分析;采集未经治疗发病学生呕吐物、粪便或肛拭子,食堂员工及食堂环境样本,发病班级饮用水及环境拭子,运用实时荧光RT-PCR进行诺如病毒核酸检测,阳性样本进行RTPCR,PCR产物纯化、测序,序列经核酸比对确认,应用Clustal X、MEGA5.1等软件分析基因序列,构建系统进化树;采用Excel2010软件建立数据库,Open Epi3.03在线软件进行统计学分析。结果 2014年11月18-24日,该校共报告病例36例,19日为发病高峰(19例)。病例集中分布在二(3)班,罹患率为55.81%(24/43),其次为二(10)班,罹患率为14.29%(6/42);症状以呕吐为主(97.22%),发热(38.89%)、腹痛(36.11%)及腹泻(8.33%)。回归性队列研究显示参加舞蹈兴趣班为发病危险因素(RR=6.67,P<0.01)。经实时荧光RT-PCR检测,16份发病学生样本中诺如病毒核酸阳性6份。序列比对结果显示,Jinshan06、Jinshan09等6株基因同源性为100%,其与GII.P17_GII.17/Kawasaki323、GII.17/Okinawa/FP027/2012等株基因同源性高达98%,均属GⅡ.17型诺如病毒,指示病毒同源。结论本次疫情是一起因密切接触引起GⅡ.17型诺如病毒感染性腹泻疫情。

Objective To analyze the epidemiological characteristics and the genotypes of pathogens in an outbreak of noroviru -induced infectious diarrhea in a primary school, to explore the possible route of transmission so as to provide scientific evidence for effective prevention and control of the epidemic as well as simultaneously provide experience for on-site disposal of the similar epidemic. Methods The uniform case definition was formulated, and the initiative case research was conducted among the students and teaching staff of the school. Descriptive epidemiological approaches and retrospective cohort study were used to identify the risk factors. Vomit and stool or anal swab samples were collected from patients without treatment. Anal swabs from the kitchen workers, drinking water samples from the classes and the environmental surface samples from the kitchen and involved classrooms were also collected. Real-time fluorescent quantitative PCR was used to detect norovirus nucleic acid, and the positive samples were amplified by RT-PCR. The PCR amplification products were purified, sequenced and then compared with sequences in Gen- Bank. The sequences were aligned by Clustal X employing MEGA 5.1 program package to construct the phylogenetic trees. The database was established by Excel 2010 software, and then analyzed by Open Epi software version 3.0.3 online. Results A total of 36 cases were reported in the school from November 18th to 24th, 2014. The peak incidence was on November 19th （ n= 19）. Grade 2 Class 3 had the highest attack rate （ 55.81%, 24/43 ） , followed by Grade 2 Class 10 （ 14.29%, 6/42）. The main symptoms included vomit 197.22% ）, fever （ 38.89% ）, abdominal pain 136.11% ） and diarrhea 1 8.33% ）. The retrospective cohort study revealed that participating in dancing class was the risk factor for the incidence （ RR = 6.67, P〈 0.01 ）. 6 out of 16 samples from the cases were found norovirus positive by real-time fluorescent quantitative PCR. The sequence alignment showed that the nucleotide sequence homology of the 6 viral stains was 100%, and they shared 98% homogeneity with GⅡ.P17_GⅡ.17/Kawasa-ki323 and GⅡ. 17/Okinawa/FP027/2012 strain, indicating these viruses were homologous and belonged to the G Ⅱ. 17 norovirus strain. Conclusion The outbreak of GⅡ. 17 norovirus-induced infectious diarrhea in the school is caused by close contact.