The incidence of medically-attended norovirus gastro-enteritis in Japan: Modelling using a medical care insurance claims database

Background: The burden of medically-attended acute gastro-enteritis (MA-AGE) that can be attributed to norovirus is not well established in Japan. Using a nationwide database of medical care insurance claims, we estimated the incidence of medically-attended norovirus-attributable gastroenteritis (MA-NGE) in Japan. Methods: The incidences of MA-NGE outpatient consultations or hospitalization in Japan were modelled on seasonal patterns of MA-AGE for unspecified causes derived from the Japan Medical Data Center (JMDC) database for the period July 2007 to June 2015. Results: Mean age-adjusted annual incidence rates (per 10,000 person-years) of MA-NGE associated with outpatient care or hospitalization were 389 (95% CI 269–558) and 13 (95% CI 9–20), respectively. Highest rates were in children under 5 years of age: 1,569 (95% CI 1,325–1,792) for outpatient consultations and 48 (95% CI 39–56) for hospitalizations. Of all gastroenteritis episodes associated with outpatient care or hospitalization, 29% and 31% were attributed to norovirus, respectively. Norovirus was estimated to be responsible for 4,964,000 outpatient visits (95% CI 3,435,000–7,123,000) and 171,000 hospitalizations (95% CI 110,000–251,000) per year across Japan. Conclusions: Incidence rates of MA-AGE are high in Japan, and norovirus-attributable disease is at least as high as in some other developed countries.