Member of a group of viruses called caliciviruses; also, known previously as "Norwalk-like viruses" which are part of an unclassified single stranded RNA virus that causes common acute infectious gastroenteritis.

The norovirus causes an infection in the stomach and the intestines, resulting in an illness called gastroenteritis, or "stomach flu". This "stomach flu" is not related to the influenza, or "flu", which is a respiratory illness caused by an influenza virus.

It should be noted that norovirus is not related to bacteria and parasites which can also cause gastrointestinal illnesses.

Norovirus is not a "new" virus, but recent interest in it is growing as more is learned about how frequently norovirus is causing illness in people.