[Epidemiological characteristics of outbreaks of norovirus-GⅡ.2, GⅡ.17 and GⅡ.4/Sydney in Guangdong province, 2013-2017].

Objective: To understand the epidemiologic characteristics of outbreaks, caused by norovirus-GⅡ.2、GⅡ.17 and GⅡ.4/Sydney in Guangdong Province from 2013 to 2017 and to provide scientific evidence for epidemic prevention and control. Methods: Incidence data of norovirus outbreaks in Guangdong from January 1(st) 2013 to November 30(th) 2017 were collected from Public Health Emergency Management Information System. RT-PCR was performed for every case of each outbreak to detect norovirus nucleic acid and gene sequencing was conducted to identify the genotype of norovirus. Characteristics of norovirus GⅡ.2, GⅡ.17 and GⅡ.4/Sydney outbreaks were analyzed. Directly standardized method was used to calculate the proportion of symtoms as diarrhea and vomitting. Results: From January 1(st) 2013 to November 30(th) 2017, a total of 167 norovirus outbreaks were reported in Guangdong, and 115 outbreaks were caused by norovirus GⅡ.2, GⅡ.17 and GⅡ.4/Sydney respectively. The outbreaks caused by norovirus GⅡ.2 accounted for 39.68 % (25/63) in primary schools, 28.57 % (18/63) in child care settings, 25.40 % (16/63) in middle schools and 6.35 % (4/63) in universities. Outbreaks caused by norovirus GⅡ.17 accounted for 41.03 % (16/39) in middle schools, 20.51 % (8/39) at workplaces, 15.38 % (6/39) in primary schools, 12.82 % (5/39) in universities, 5.13 % (2/39) in communities and child care settings respectively. The outbreaks caused by norovirus GⅡ.4/Sydney accounted for 53.85 % (7/13) in universities, 15.38 % (2/13) in child care settings and at workplaces respectively, 7.69 % (1/13) in primary schools and middle schools respectively. The outbreaks caused by norovirus GⅡ.2 had 77.78 % (49/63) of contact transmission, 17.46 % (11/63) of food-borne transmission. The outbreaks caused by norovirus GⅡ.17 showed 53.85 % (21/39) of food-borne transmission, 15.38 % (6/39) of contract transmission, 12.82 % (5/39) of water-borne transmission. The outbreaks caused by norovirus GⅡ.4/Sydney had 53.85 % (7/13) of food-borne transmission, 38.46 % (5/13) of the contact transmission. In terms of the clinical manifestations, the standardized proportion of vomit was 73.76 % and the proportion of diarrhea was 42.85 % in cases infected with norovirus GⅡ.2, the proportion of standardized of vomit was 76.37 % and the proportion of diarrhea was 51.40 % in cases infected with norovirus GⅡ.17, with the standardized proportion of vomit was 54.10 % and the proportion of diarrhea was 55.95 % in cases infected with norovirus GⅡ.4/Sydney. Conclusions: The outbreaks caused by norovirus GⅡ.2 through contact transmission mainly occurred in primary schools, child care settings and middle schools. The outbreaks caused by norovirus GⅡ.17 through food-borne transmission mainly occurred in middle schools and at workplaces. The outbreaks caused by norovirus GⅡ.4/Sydney food-borne transmission and contact mainly occurred in universities.