You can be contagious from a few days to two weeks, depending on which virus is causing your stomach flu (gastroenteritis). A number of viruses can cause gastroenteritis, including noroviruses and rotaviruses. The contagious period — the time during which a sick person can give the illness to others — is slightly different for each virus.
- Norovirus. With norovirus — the most common cause of viral gastroenteritis in adults — you're contagious from the moment you begin to feel ill. Symptoms appear within one to three days of exposure. Although you typically feel better after a day or two, you're contagious for at least three days after you've recovered. Some people may be contagious for up to two weeks after recovery. Also, children are often contagious for a longer period than are adults.
- Rotavirus. Symptoms of rotavirus — the leading cause of viral gastroenteritis in infants and young children — appear one to two days after exposure. But you're contagious even before you develop symptoms, and you typically remain contagious for two weeks after you've recovered. Children are often contagious for a longer period than are adults.
The viruses that cause gastroenteritis are spread through close contact with infected people, such as by sharing food or eating utensils. Washing your hands or using hand sanitizer is the most effective way to stop the spread of these viruses to others.