Noroviruses are highly contagious viruses that cause vomiting and diarrhea. In fact, most nonbacterial gastroenteritis infections are caused by noroviruses. These viruses are transmitted by the fecal-oral route and the source of infection is often contaminated food or water; for example, eating fresh or frozen berries without heating them first has been identified as a typical way of catching the disease. The virus also spreads easily when one comes into contact with infected individuals and from surfaces that they have touched. This means that the virus easily spreads among groups of people, for example in schools, in hospitals or even at home. The Norovirus genus belongs to the Caliciviridae family of positive-sense single stranded RNA viruses. Other genera in this family are Vesivirus, Lagovirus, Sapovirus and Nebovirus. In addition to humans, different caliciviruses infect vertebrates such as cats, pigs, rabbits and cattle.