Characteristics of epidemic dynamics of norovirus caused diarrhea in Longgang district of Shenzhen

ObjectiveTo understand the epidemic dynamic characteristics and transmission route of norovirus caused diarrhea outbreaks in Longgang district of Shenzhen and provide theoretical basis for the prevention and control of norovirus caused diarrhea outbreaks.

MethodsDescriptive epidemiological analyses were conducted on the epidemiological and etiological characteristics of norovirus caused diarrhea outbreaks in Longggang from July 2014 to June 2017, and the epidemic dynamic characteristics and intensities were statistically analyzed.

ResultsIn the past 3 epidemic seasons, 47 norovirus caused diarrhea outbreaks occurred in Longgang, involving 635 cases, and the attack rate was 12.92%. Winter and spring were the seasons with high incidence of norovirus caused diarrhea outbreaks, especially from December to February. The cases were mainly young children, followed by students. The average detection rate of norovirus in biological samples was 33.33%, and the predominant strain belonged to GⅡ type. The epidemics usually affected 6 to 99 persons. The average interval between onset and reporting of the first case was 2.14 days, and the average duration of the outbreaks was 2.68 days, and the case number increased by 2–25 per day. The mean of the basic reproductive number was 9.91 (5.00－17.00). The average basic reproductive numbers in child care settings, schools and public service settings were 9.72 (n＝39), 12.00 (n＝5) and 8.34 (n＝2) respectively, the differences were not significant (F＝1.209, P＝0.308). Forty four outbreaks (93.62%) transmitted from person to person, including 3 foodborne transmissions associated with infected cooks, and no waterborne epidemic was found. The epidemic intensity during 2016 winter－2017 spring was obviously stronger compared with the previous two epidemic seasons.

ConclusionNorovirus has a large basic reproductive number in epidemic, indicating that it is easy to cause a large-scale outbreak in child care settings and schools. It is necessary to take different prevention and control measures for the transmission sources and routes in the early stage of the epidemic.