Emergence of GI.6 Outbreaks in a High School in Fangshan District, Beijing, China

Abstract

[Background] An outbreak of gastroenteritis happened in a high school in Fangshan District, Beijing, China in March 2016，in which 44 students developed the symptoms of vomiting, nausea, diarrhea and abdominal pain. Epidemiological investigation, laboratory investigation and Statistical analysis were conducted to identify the agent and source of this outbreak.[Methods] A case–control study was performed to discover the factors associated with this infection. Questionnaires and clinical data from those infection-exposed people were assessed. Here an outbreak case was defined as a student who developed at least three following symptoms: diarrhea, vomiting, abdominal pain and nausea in 72 hours after the lunch on 2nd March., and controls were those who study or work in the school but did not have lunch on the day. Samples (Stool samples, rectal swabs and vomit samples) from infection-exposed students and controls, as well as environmental samples like food were collected to test for the existence of any suspicious bacteria or viruses. Detection of norovirus wasdone by real-time TaqMan RT-PCR and sequence analysis. Chi-square test was used to decide whether those differences could be of any statistical significance. [Results] The total number of respondents with complete data was 44. An epidemiological data combined with the epidemic curve indicated that the outbreak started initially from a point source type, and was followed by a secondary transmission. Five stool samples, three rectal swabs and one vomit sample from case group turned out to be positive for norovirus genotype I by real-time PCR, and two asymptomatic food handlers in control group were positive for NoV GI. Sequence analysis of GI positive sample confirmed that the norovirus GI.6 variant was the etiological agent of the outbreak. Comparasion between the tested results from samples of those students who had lunch in school canteen and those who did notindicates that the difference of incidence was of statistical significance (P<0.01, 95% CI:4.22-324.41). Food and environmental samples were tested to be bacteria-negative. [Conclusions] Our result suggested that the etiological agent of the outbreak was norvirus GI.6, which leads to gastroenteritis. We identified that asymptomatic infected food handlers were most likely to be the source of the outbreak. Therefore，hand hygiene practices strict adherence to regulations and access to hand washing facilities should be strengthened.