Noroviruses are a group of related viruses that are highly contagious. You can get norovirus from an infected person, contaminated food or water, or by touching contaminated surfaces. Infection with these viruses affects the stomach and intestines and causes an illness called gastroenteritis (inflammation of the stomach and intestines).

Anyone can be infected with noroviruses and get sick. You can get norovirus illness more than once during your lifetime. The illness often begins suddenly. You may feel very sick, with stomach cramping, nausea, vomiting, or diarrhea.

Noroviruses are the most common cause of gastroenteritis in the United States. Each year in the United States, norovirus causes between 19-21 million cases of acute gastroenteritis (about 1 in every 15 individuals will get norovirus illness annually); 1.7–1.9 million outpatient visits and 400,000 emergency department visits, primarily in young children; and about 56,000–71,000 hospitalizations and 570-800 deaths, mostly among young children and the elderly.