| Objectives:To study the epidemic characteristics,trends and risk factors of norovirus outbreaks in different places and different modes of transmission and explore the applicability of Kaplan Criteria in the early stage of prevention and control of norovirus outbreaks in China.Methods:1.From 2014 to 2018,the information and investigation report of other infectious diarrhea,food poisoning and water pollution emergency had been downloaded from the National Public Health Emergency Management Information System(PHEMIS).Then we established a database of norovirus outbreaks,and descriptive epidemiological methods were used to analyze the frequency,seasonality,settings and transmission modes.2.We linked the spatial data of outbreaks reported by provinces(municipalities or autonomous regions)with the population,the number of outbreaks and illnesses and norovirus genome.ArcGIS 10.3(Esri,Redlands,CA,USA)were used to produce outbreak distribution maps for comparing epidemic characteristics and trend in different provinces.3.The method of Spearman’s Rank Correlation Analysis was used to explore the correlation between the duration of the outbreaks,the number of outbreaks and reporting timeliness.4.The proportion of illnesses’ clinical symptoms was summarized and analyzed.Then we searched CNKI(China National Knowledge Infrastructure),Wanfang Data and PubMed for studies that contain duration of illness or incubation of norovirus,with the onset time of the outbreaks of norovirus acute gastroenteritis in China from 2014 to 2018.So that we could explore the applicability of Kaplan Criteria in the early prevention and control of norovirus outbreak in China.Results:1.Overall,915 norovirus outbreaks were reported by PHEMIS during 2014-2018.these outbreaks were associated with 45 527 illnesses and 1 927 419 exposed people,but no deaths.The number of outbreaks increased from 58 in 2014 to 324 in 2017,showed an increasing trend with an average annual growth rate of 54%.The number of illnesses was increased with an average annual growth rate of 25%in these 5 years.Norovirus outbreaks have been reported throughout the year,with high number in winter and spring.There were two peaks each year focusing on February-March and November-December,and the number of outbreaks were at the lowest point on July-August,January or February.Norovirus outbreaks reported in 2014-2018 occurred in 26 provinces(municipalities or autonomous regions).The largest number of reported outbreaks were in Guangdong(196,21%),followed by Jiangsu(195,21%),Chongqing(118,13%),Anhui(58,6%)and Hunan(53,6%).Of the 915 outbreaks,550(60%)reported the results of the norovirus genomic test results.Among them,482(88%)were infected in GII group,33(6%)in GI group,and 35(6%)mixed infection of GI group and GII group.2.Norovirus reported outbreaks in China mainly occurred in primary schools(356,39%),secondary schools(203,22%),childcare institutions(199,22%),and followed by universities(50,5%),other places(31,3%),other schools(30,3%),restaurants(17,2%),communities and families(17,2%),hospitals(7,1%)and transportation equipment(5,1%).These outbreaks mainly transmitted by person-to-person(622,68%),followed by multiple mode of transmission(81,9%),foodborne(46,5%)and waterborne(36,4%)·130 outbreaks’transmission,accounting for 14%,were unknown.A total of 669 outbreaks involved person-to-person transmission.Improper handling of vomit was the main risk factor.There were 114 outbreaks involving foodborne transmission,58%of which were associated with food contamination with infected or implicitly carried food handers.There were 57 outbreaks involving waterborne transmission.Contamination of self-providing well wate or secondary water-supply system was a common risk factor with 24(42%)outbreaks.3.The median duration of norovirus outbreaks was 5 days(IQR:2-8 days).The median number of illnesses in a single outbreak was 34(IQR:22-57).The median reporting interval time was 3 days(IQR:2-5 days).There was a positive correlation between the duration of outbreaks and the reporting interval time(r=0.50,P<0.01).4.Clinical symptoms of norovirus illnesses included vomiting,diarrhea,abdominal pain,nausea.The median proportion of vomiting illnesses in a outbreak was 76%(IQR(Interquartile Range):55%-93%),median proportiorn of other symptoms included diarrhea 62%(IQR:36%-81%)5 abdominal pain 51%(IQR:0%-63%),nausea 41%(IQR:28%-65%)and fever 17%(IQR:7%-34%)respectively.Conclusions:1.The trend showed an increase in the number of norovirus reported outbreaks and illnesses from 2014 to 2018 in China,the epidemic were characterized by extended distribution,prolonged peak duration,high incidence in winter acnd spring and high incidence every other years.2.Norovirus outbreaks mainly occurred in schools and childcare facilities,and the main transmission mode was person-to-person.Improper handling of vomit was the most common risk factor of person-to-person transmission.Foodborne transmission often occured from infected or implicitly carried food handers.Waterborne transmission mainly related to the contamination of the self-providing well wate or secondary water-supply system by norovirus.3.Norovirus outbreak should be reported early,and Kaplan Criteria can be used as the basis for early detection,early reporting and early treatment of norovirus outbreak. |
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