Rotavirus is a virus that causes gastroenteritis (inflammation of the stomach and intestines). The virus passes in the stool (poop) of infected people before and after they have symptoms. Children can become infected if they put their fingers in their mouths after touching a contaminated surface, like a toy. Rotavirus causes severe watery diarrhea, often with vomiting, fever, and abdominal pain. In babies and young children, it can lead to dehydration (loss of body fluids). It is the leading cause of severe diarrhea in infants and young children worldwide. The rotavirus vaccine is one of the best ways to prevent this infection.