A condition caused by norovirus, characterized by nausea, vomiting, diarrhoea and giddiness, which occurs in winter epidemics. Outbreaks usually involve whole families or may affect communities like schools. It may also occur in closed communities such as cruise ships. The incubation period is 24—48 hours, and attacks seldom persist for more than 72 hours. Humans are the only known hosts of the virus and infection can be acquired via contaminated food or water or, more commonly, from an infected individual via the faeco-oral route, aerosol-spread and fomites.