Almost 1,000 people fell ill in a Campylobacter and Sapovirus outbreak in China in 2021, according to a recently released study.

The outbreak involved 996 patients and had two peaks over a 17 day period. Through case-control studies, scientists identified exposure to water from a secondary water supply system as a significant risk factor.

Among 83 patients, 49 samples tested positive for Campylobacter coli, 39 tested positive for human Sapovirus, and 27 were positive for both pathogens.

Details on the first reported outbreak in China with infection by Campylobacter coli and Sapovirus were published in the journal China CDC Weekly.

In July 2021, a hospital in Beijing identified 13 patients with acute gastroenteritis in the same school. Epidemiological investigations later revealed 996 patients, including 958 students and 38 staff members. 

The most common symptoms were abdominal pain, diarrhea, nausea, vomiting, and fever. A total of 828 questionnaires were completed, including 341 gastroenteritis cases and 487 controls.

Water contamination source
One direct drinking water (DDW) system supplied by a secondary water supply system (WSS-S) was identified in the school building. This DDW system offered unboiled direct drinking water (UDDW) and boiled. The water source for WSS-S is a groundwater source well (WSW) within the campus. One hotel on the same campus also has its own secondary water supply system (WSS-H), which uses the WSW as its water source.

Both WSS-H and WSS-S have separate facilities including a water storage tank, water pump, and pipeline. The WSS-H conducted disinfection using chlorine dioxide and the storage tank and pump were inside the hotel. The water quality from WSS-H was supervised effectively.

However, the water storage tank and pump of WSS-S was not inside the school and lacked effective management. The sewage well was uncovered and did not have protective facilities during rainfall, said researchers.

Based on findings from case-control studies, exposure to unboiled direct drinking water from the contaminated secondary water supply system increased the risk of illness. The nearby garbage station and sewage well were likely sources of contamination.

After a rainstorm, some students reported the water in the school appeared turbid and had an unpleasant odor. After drinking water was replaced with commercially bottled water, the number of patients decreased significantly. 

The antibiotic resistance profile of 17 Campylobacter coli isolates showed co-resistance to nalidixic acid, ciprofloxacin, streptomycin, and tetracycline.

“Results of aerobic plate counting and coliform detection indicated that the water samples from the WSS-S were of poor quality. But neither Campylobacter coli nor human Sapovirus were identified in the water samples. Waterborne outbreaks often occur on a large scale and involve complex processes of pathogen examination and tracing. This report emphasizes the significance of ensuring the safety of drinking water, particularly in secondary supply systems,” said scientists.

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