Stomach flu is highly contagious and can spread easily from person to person. These viruses often can be found in the stool or vomit of infected people. Transmission can occur in one of several ways, including:
- Eating foods or drinking liquids that are contaminated with a stomach flu virus
- Having direct contact with another person who is infected and showing symptoms (for example, when caring for someone with the illness, or sharing food or eating utensils with someone who is ill)
- Touching surfaces or objects contaminated with a virus and then putting your hands in your mouth.
(Click Stomach Flu Transmission for more information.)
When a person becomes infected with stomach flu, the virus begins to multiply within the small intestine. After approximately 1 to 2 days (depending on the virus), symptoms can appear. This period between the transmission of the virus and the start of symptoms is the "stomach flu incubation period." In some cases, the incubation period can be as short as 4 hours.
(Click Stomach Flu Incubation Period for more information.)
Whether or not a person is contagious during the incubation period will depend on which virus he or she is infected with. For example, with a rotavirus infection, the person is contagious during the incubation period. He or she is also contagious while experiencing symptoms. Once the diarrhea has ended, a person with rotavirus gastroenteritis is no longer contagious.
With a norovirus infection (including Norwalk virus), a person is not usually contagious during the stomach flu incubation period. People infected with norovirus gastroenteritis are usually contagious from the moment they begin feeling ill to at least 3 days after recovery. Some people may be contagious for as long as 2 weeks after recovery.