Norovirus is a virus that causes nausea, vomiting, and diarrhea, known as acute gastroenteritis or “stomach flu.”; Norovirus is the most common cause of food-borne disease outbreaks in the U.S. Norovirus is highly contagious and often occurs in outbreaks where people are in close contacts, such as dorms, cruise ships, or nursing homes.; Symptoms of norovirus typically last for one to three days.