Rotavirus is an RNA virus in the Reoviridae family. It infects many types of mammals and birds as well as humans. Rotavirus is the most frequent cause of infectious diarrhea of infants and young children. Symptoms include diarrhea (65%-100% of cases), fever, and vomiting (48%-92% of cases). Vomiting may precede diarrhea (usually by less than 24 hours) in 34%-55% of patients. Peak infection rates in the United States are in winter months but are equally distributed in tropical areas. Rotavirus has been reported to cause 36%-50% of gastroenteritis severe enough to need hospitalization in nontropical countries. Rotavirus can be identified in the stool of considerable numbers of hospitalized children without diarrhea and some clinically healthy young children, especially in day-care centers or nurseries (about 10%-20%; literature range, 2%-71%). Adults may also become infected (especially those in contact with infected infants or children, 20%-36% in several studies); the majority are asymptomatic, but some develop diarrhea. Diarrhea tends to be more common and severe in the elderly. Some patients with symptomatic rotavirus infection also have respiratory symptoms, either before or concurrent with diarrhea (although this was not present in some studies).

Rotavirus has not yet been cultured. The gold standard for diagnosis is electron microscopy (EM) of stool specimens. Same-day diagnosis can be obtained from stool specimens using ELISA or LA antigen-detection methods. Sensitivity of the various kits available is about 90% (range, 61%-100%), compared to EM. There is a significant difference in sensitivity between some of the kits.