Causes

You're most likely to contract viral gastroenteritis when you eat or drink contaminated food or water, or if you share utensils, towels or food with someone who's infected.

A number of viruses can cause gastroenteritis, including:

• Noroviruses. Both children and adults are affected by noroviruses, the most common cause of foodborne illness worldwide. Norovirus infection can sweep through families and communities. It's especially likely to spread among people in confined spaces. In most cases, you pick up the virus from contaminated food or water, although person-to-person transmission also is possible.
• Rotavirus. Worldwide, this is the most common cause of viral gastroenteritis in children, who are usually infected when they put their fingers or other objects contaminated with the virus into their mouths. The infection is most severe in infants and young children. Adults infected with rotavirus may not have symptoms, but can still spread the illness — of particular concern in institutional settings because infected adults unknowingly can pass the virus to others. A vaccine against viral gastroenteritis is available in some countries, including the United States, and appears to be effective in preventing the infection.

Some shellfish, especially raw or undercooked oysters, also can make you sick. Although contaminated drinking water is a cause of viral diarrhea, in many cases the virus is passed through the fecal-oral route — that is, someone with a virus handles food you eat without washing his or her hands after using the toilet.