You’re most likely to get viral gastroenteritis when you eat or drink contaminated food or water. You may also be likely to get gastroenteritis if you share utensils, towels or food with someone who has one of the viruses that cause the condition.

Many 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. But it can also spread between people who are in close contact or who share food. You can also get the virus by touching a surface that’s been contaminated with norovirus and then touching your mouth.

• 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. It can also spread through contaminated food. The infection is most severe in infants and young children.

Adults infected with rotavirus may not have symptoms, but can still spread the illness. This is of particular concern in institutional settings such as nursing homes because adults with the virus 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. Contaminated drinking water is a cause of viral diarrhea. But in many cases, the virus is passed when someone with a virus handles the food you eat without washing his or her hands after using the toilet.