Published online by Cambridge University Press: 07 December 2009
Noroviruses are single-stranded RNA viruses and belong to the family Caliciviridae. There are three genogroups of noroviruses. New variants emerge every few years.
Route of spread
Noroviruses most frequently spread by the ingestion or inhalation of vomit. Patients frequently have no prior warning that they are about to vomit, which results in environmental contamination.
Noroviruses are also transmitted by contaminated food (e.g. bivalve molluscs, such as cockles and oysters, contaminated by human sewage in sea water). Symptomatic food handlers can also contaminate food, resulting in outbreaks.
Norovirus infection is common and 90% of adults have been infected at some time in their lives. Immunity lasts for less than a year, and reinfection can occur with the same or different strains.
24–48 hours after contact with a contaminated environment or eating contaminated food.
From onset of symptoms to 48 hours after symptoms stop.
Noroviruses are associated with diarrhoea and vomiting (especially projectile vomiting).
Noroviruses cause large outbreaks in hospitals, cruise ships and in the community, especially in schools and nursing homes. Outbreaks occur more frequently in the winter (winter vomiting disease), but when new variants emerge outbreaks in the summer occur.