: Norovirus is a common cause of non-bacterial acute gastroenteritis worldwide, and norovirus infection shows symptoms such as vomiting and diarrhea in patients of all age groups. Mass outbreaks of norovirus infection have been recently reported in Korea. Herein, we investigated the epidemiological characteristics of acute norovirus gastroenteritis. Methods : We analyzed 11,219 fecal specimens of patients with acute gastroenteritis symptoms from the 5 participating hospitals for 3 yr (March

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... -February 2010) to determine positive rates of detection using RIDASCREEN Norovirus ELISA (R-Biopharm AG, Germany) kit by year, prevalence season, sex, age, and region. Results : Norovirus infection was prevalent during autumn and winter, and 13.0% specimens were positive for the infection. The positive rates of norovirus detection were 16.2%, 13.8%, and 9.9% in 2007, 2008, and 2009, respectively, and they tended to decrease every year. In 2007 and 2008, the epidemicity of norovirus started from October, reached its peak in November, and lasted until January. However, in 2009, it started from December, reached its peak in January, and lasted until February. Most patients were 0-3 yr old and this patient group had the highest positive rate. There was no significant inter-regional difference among the subjects. Conclusions : We performed epidemiological analysis of norovirus infection using ELISA assay. Reverse transcription-PCR indicated higher prevalence of norovirus infection as compared with that reported before 2007. Further studies are warranted to examine the changes observed in the epidemic period of 2009.