Surveillance of the 'bud event of norovirus-associated gastroenteritis' in schools: does it work in the prevention of norovirus infection outbreaks in Shanghai?

Outbreaks of norovirus-associated gastroenteritis have been reported in schools in recent decades in China. For early warning and response to infectious disease outbreaks, the Shanghai Infectious Diseases Bud Event Surveillance System (IDBESS) was established in 2016. Bud event is a term used for the early sign of a potential infectious disease outbreak in public settings when the first few cases appear. This study aimed to describe the epidemiological characteristics of Norovirus-associated gastroenteritis bud events from June 2016 to December 2017 and to understand factors influencing the severity of events. Data were extracted from the IDBESS, supplemented by field investigations and school absence surveillance. In total, 189 bud events of Norovirus-associated gastroenteritis were reported in schools and kindergartens, affecting 3827 individuals and 52.38% happened in primary schools. The attack rate of Norovirus-associated gastroenteritis was 3.82% on average in students in the affected schools. In each event, case numbers varied between 5 and 148, with a median of 16. The duration of bud events lasted for 2 days on average. School absence happened in 47.93% (1797/3749) of affected students and the average duration of absence was 3.07 days. It was found that a longer delay before reporting was associated with a longer-lasting duration of bud event (OR = 2.25, 95% CI: 1.65, 3.07). In conclusion, ascribed to the sensitive threshold for alerting and the timely field investigation, the surveillance of bud events of Norovirus-associated gastroenteritis is effective in the control of Norovirus infection among preschool children and students in Shanghai.

[Epidemiological analysis on bud-events of Norovirus-associated infectious diarrhea in Shanghai, 2018].

Objective: To analyze the epidemiological characteristics related to Norovirus-associated infectious diarrhea bud events in Shanghai, and to discuss the value of bud events surveillance, so as to help Norovirus-associated infectious diarrhea control, prevention and to improve the surveillance system on bud events. Methods: Data related to 142 Norovirus-associated infectious diarrhea bud events were gathered from 16 districts of Shanghai areas in 2018 and were analyzed. Results: There were 2 peaks, April and November for 142 Norovirus-associated infectious diarrhea bud events reported in 2018. 98.59% (140/142) of the bud events occurred in schools and kindergartens. 80.28% (114/142) of the bud events would involve 6-19 cases per each event. The median time duration between the onset date of the first case and the reporting date of the event was 2 days and the median event duration was 7 days. The bud event scale and regional incidence of bud events as well as the reporting timelines were influential factors on the duration of the bud events. Conclusions: Two peaks, spring and winter bud events of the Norovirus-associated infectious diarrhea were seen in Shanghai in 2018. Schools and kindergartens were to be prioritized locations for control and prevention of Norovirus-associated infectious diarrhea bud events. Surveillance system was proved to have contributed to the early detection, reporting and control of bud events.