Objective To determine the epidemiological characteristics and risk factors of a norovirus GII.17 outbreak in Minhang District of Shanghai in 2018， and provide evidence for prevention and control measures of norovirus infection.
Methods Descriptive epidemiological analysis was performed. In addition， a retrospective cohort study was conducted to determine the risk factors.
Results From May 30th to June 1st of 2018， a total of 132 cases （126 clinical cases and 6 confirmed cases） were documented，with an attack rate of 29.20%（132/452）.All cases were children in a kindergarten， with the average age of 5 years and 43.9% being male. The cases were reported in all the classes， with no clustering by class or floor．The epidemic curve was characterized by a point source exposure， which was estimated to be probably between 7 AM on May 30thand 0：30 AM on May 31st. The retrospective cohort study showed that the attack rate significantly differed between the children who had taken and did not take the school lunch （RR=∞） on May 30th，and those who had taken and did not take seafood noodles （RR=4.11， 95%CI：1.09-15.55） （P<0.05）. Among a total of 73 specimens， six specimens collected in child cases and one specimen in an asymptomatic chef tested positive for GII.17 type of norovirus. In addition， one retained food specimen of seafood noodles was positive for Aeromonas hydrophila. Viral shedding in the asymptomatic chef remained over 30 days.
Conclusion The outbreak was caused by seafood noodles contaminated by norovirus. It warrants enhancement in the regulation of food safety in canteens and regular examination of norovirusinfection in catering industry employees.
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