ABSTRACT
<p><b>OBJECTIVE</b>To investigate the epidemiology characteristics of norovirus among diarrheal outpatients in China.</p><p><b>METHODS</b>Diarrhea cases were monitored at emergency/outpatient departments at 173 hospitals in 27 provinces of China, with clinical and epidemiological data, and fecal specimens collected and sent to 58 network-laboratories to detect norovirus by RT-PCR method, and to analyze the positive rate of norovirus in various regions, population and time during 2009-2013.</p><p><b>RESULTS</b>11.6% of the 34 031 diarrheal cases under surveillance were found with norovirus. Age group of 6-23 month-old children and that of people over 45 years old were found with the highest positive percentage, 13.7% and 12.4% respectively. Positive percentage of norovirus peaks in autumn and winter in a year; it peaks in mid-temperate zones (10.7%) and warm-temperate zones (11.6%) in winter. It peaks in sub-tropical zones in autumn (14.3%). The most prevalent genogroups detected were norovirus G II, accounting for 89.9% of identified strains.</p><p><b>CONCLUSION</b>Norovirus affects all ages and was most prevalent in children and the elderly among diarrhea outpatients. Norovirus' positive percentage showed strong seasonal pattern, and peaks at different times of a year in different climate zones of China. Since no effective preventive measures existed, further study on norovirus epidemiology and intervention strategies should be conducted in future.</p>