Norovirus

Noroviruses cause diarrhoea. They are transmitted through the mouth or nose, causing copious vomiting and severe diarrhoea. Noroviruses occur throughout the world. No medication or vaccine is available to prevent infection. 

Pathogen and transmission

Noroviruses are responsible for most cases of non-bacterial diarrhoea. As they are highly infectious (between 10 and 100 viruses are sufficient for transmission), outbreaks of infection occur wherever people live in close confinement. This is particularly the case in families, care homes, hospitals, barracks, cruise ships and kindergartens. The viruses are transmitted via the mouth, by contact with the skin (e.g. contaminated hands) or objects (e.g. contaminated door handles), by inhaling fine particles in the air (e.g. after someone has vomited) or by consuming contaminated food or water. Noroviruses are highly resistant to environmental factors (e.g. temperature fluctuations) and can remain infectious for more than 12 days on contaminated surfaces.

Clinical picture

The condition usually develops 12 to 48 hours after infection, and usually involves an abrupt onset marked by copious vomiting and diarrhoea and often accompanied by stomach and muscle pain and headaches. Some patients develop fever. Recovery takes two to three days. Treatment consists mainly of ensuring an adequate fluid intake.

Frequency and distribution

Noroviruses occur throughout the world. In Europe, infections occur mainly in the winter months, although they can happen at any time during the year if viruses are imported from other parts of the world. In Switzerland, there are an estimated 400,000 cases of diarrhoea and sickness due to norovirus each year. The reporting system operated by the Federal Office of Public Health only registers clusters of cases, e.g. of norovirus infection. There is no obligation to report individual cases.

Prevention

There is no vaccine or medication to treat norovirus. Good hand hygiene is important, which means washing thoroughly with soap, especially after using the toilet. In addition, objects and surfaces that have come into contact with faeces or vomit should be cleaned and subsequently disinfected, e.g. with diluted (0.1 percednt) bleach. Bleach products sold for domestic use contain a concentration of 2.5 percent and need to be diluted to 0.1 percent (250 ml of the commercial product in 6 litres of water). Infected individuals should not prepare meals. Infected individuals who work in vulnerable institutions (retirement homes, hospitals, restaurants, schools), should stay away from work for at least two to three days after the symptoms have disappeared and should continue to maintain good hygiene.

Documents

Documents on this subject are available in German and French.

Last modification 06.11.2023