An outbreak of norovirus infection associated with contamination ofsecondary water supply in a hospital

Objective To identify the infection source, transmission route and risk factors of an acute gastroenteritis outbreak in a hospital in Suzhou, Jiangsu province. Methods The cases were searched according to case definitions. A case-control study was conducted to test the hypothesis for this outbreak. Ten stool samples and 1 vomit sample were collected for the detection of norovirus using RT-PCR. Nine drinking water samples were collected for physiochemical and microbiological detections. Results The outbreak lasted for 7 days, and 406 cases were identified. The attack rate (AR) in nurses was highest (18%) and lowest in office staff (1.4%). The ARs in people in secondary water supply, tap-water and bottled water areas were 14%-21%, 0-5.3% and 1.4%, respectively. 90% of the cases and 47% of the controls had drunk water from secondary water supply system (OR=10, 95%CI:2.30-62.00). Up to 90% of stool samples (9/10)were norovirus positive and 22.2% of water samples from secondary water supply system (2/9)were norovirus positive. Total microbial counts, coliforms and the detection rate of Escherichia coli were highly exceed the standard in the water samples from secondary water supply system. The temperature of water from electric water heater was 78-81℃. Conclusion This outbreak was caused by the contamination of norovirus genotype I in the water tank of secondary water supply system.