Norovirus is an extremely common and highly contagious virus which causes gastroenteritis (an inflammation of the stomach and intestines). Symptoms of norovirus include nausea, vomiting and diarrhea. Some people may also experience headache, mild fever and abdominal cramps. It is sometimes known as the "24 hour stomach bug." Symptoms usually last between one and three days and generally resolve without treatment or long term consequences. The incubation period of the virus averages about 24 hours and people infected with the illness typically remain contagious for 72 hours after they have recovered.