These RNA viruses cause gastroenteritis primarily in infants and young children, similar clinically to rotavirus infection; sometimes as severe as rotavirus but often somewhat milder. Cluster outbreaks in institutions and sporadic occurences have been reported. One report indicated that calciviruses cause 3% of gastroenteritis in U.S. day-care centers. Some cluster infections in adults from contaminated food or water have been reported. Diagnosis can be made through EM of stool. Some homemade EIA methods have been described. High antibody positivity rates (90%-100%) have been found by late childhood or early adulthood.