Infections occur year-round, with a slight increase in summer. Incubation is 8 to 10 days. Less is known about the epidemiology of non-Norwalk calicivirus and astrovirus. Both can infect persons of all ages but usually infect infants and young children. Calicivirus infections occur year-round, whereas gastroenteritis caused by astrovirus is most common in the winter.
Transmission is via the fecal-oral route.
Incubation is 1 to 3 days for both viruses. The majority of infections caused by viral enteropathogens are asymptomatic. Infants and young children with rotavirus gastroenteritis may develop severe watery diarrhea lasting 5 to 7 days and leading to isotonic dehydration. Norwalk virus typically causes acute onset of vomiting, abdominal cramps, and diarrhea, with symptoms lasting only 1 to 2 days. In children, vomiting is more prominent than diarrhea, whereas in adults, diarrhea usually predominates.