Worldwide molecular epidemiology of norovirus infection.

Norovirus (NoV) is recognised as one of the emerging viruses causing infection in humans. It is the leading cause of outbreaks of viral gastro-enteritis worldwide. In children, NoV plays an increasing and important role in enteric infection, apart from rotavirus, especially in the post-rotavirus vaccine era. NoV-infected children usually present with typical clinical manifestations of acute viral gastro-enteritis, including vomiting and watery diarrhoea, and paediatric patients are more liable to have dehydration requiring hospitalisation. Other than these symptoms, severe or atypical complications associated with NoV infection include infantile convulsion, necrotising enterocolitis, and, rarely, disseminated disease involving multiple organs. Although most symptoms of NoV infection are self-limiting, recurrent infection is not uncommon in children as well as in the elderly. The rapid evolution and complex genetic diversity of NoV makes for difficulty in identification, classification and surveillance of the virus. Using molecular biological methods, clearer genetic and molecular features of the circulating NoV are now recognised. The emerging GII.4 genotype is currently responsible for 60-90% of outbreaks worldwide. Rapid transmission of NoV from person-to-person makes the infection difficult to control. In addition to personal hygiene such as hand-washing, prevention of NoV will depend largely on the development of an effective vaccine. Given the rapid evolution of the virus, continued molecular epidemiological surveillance is important.