Norovirus is a viral infection that is a common cause of diarrhea and vomiting sickness in the United States. It is spread primarily by infected people or contaminated food and water. Stool and vomit are the common places where the virus develops. Any food, drink, animal, or person that may have contact with stool or vomit can become exposed. Symptoms such as a headache and low-grade fever may also be present.