Viruses
A common cause of diarrhea is viral gastroenteritis (often called the "stomach flu," it also can cause nausea and vomiting). Many different viruses can cause viral gastroenteritis, which can pass through a household, school, or day-care center quickly because it's highly infectious. Although the symptoms usually last just a few days, affected kids (especially infants) who are unable to get adequate fluid intake can become dehydrated.
Rotavirus infection is a frequent cause of viral gastroenteritis in kids. Rotavirus usually causes explosive, watery diarrhea, although not all will show symptoms. Rotavirus has commonly caused outbreaks of diarrhea during the winter and early spring months, especially in child-care centers and children's hospitals, however, a vaccine now recommended for infants has been found to prevent approximately 75% of cases of rotavirus infection and 98% of the severe cases that require hospitalization.
Another group of viruses that can cause diarrhea in children, especially during the summer months, are enteroviruses, particularlycoxsackievirus.