[Norovirus and its increasing clinical importance].

Over the last years, there has been an increasing acknowledgement of the impact on people’s health of infections by Norovirus. In the U.S.A. it is considered the most frequent cause of gastroenteritis, producing 19–21 millions of infections, 56,000–71,000 hospitalisations, and 570–800 deaths per year.1 Moreover, Norovirus is considered the main cause of outbreaks and sporadic cases of nonbacterial gastroenteritis in patients of all ages.2 In industrialised countries, the incidence of this condition among ambulatory patients is estimated to be between 21 and 92 every 10,000 inhabitants, with hospitalisation rates from 1.2 to 2.4 every 10,000 inhabitants and mortality rates from 0.19 to 0.40 every 10,000 inhabitants.3 Outbreaks mainly take place in health care centres, schools, restaurants, cruises long-term health care centres, and daytime centres.2 Only in the U.S.A., the estimated incidence of this disease in cruises is 25.6 every 10,000 inhabitants, constituting the main cause of gastroenteritis.4 This disease is more frequently seen in developing countries as a result of poor sanitary and hygienic conditions, although there are discrepancies in terms of rates, probably due to the difficulties in reaching a diagnosis, given the concomitance of other gastrointestinal diseases, both bacterial and parasitic.3 At-risk population: the incidence rate of this disease is very high among children under 5 years of age (2140 every 10,000 inhabitants); this virus is responsible for 18% of diarrhoea processes,3 and constitutes the second cause of endemic diarrhoea within this population after rotavirus.5 Population at risk also includes people over 65 years of age and immunosuppressed patients.3,6 Among humans, the virus has a person-to-person transmission (faecal-oral and vomit-oral) or, indirectly, through the consumption of foods and water or through environmental transmission. Zoonotic transmission is unusual, since this virus is highly selective in terms of its hosts. Person-to-person transmission is responsible for 90% of Norovirus outbreaks in health care centres. In order for food and water consumption and environmental transmission to be viable, the food, water or fomite in question must have been previously contaminated with viral particles from an infected human.7