The results of antibody studies correlate with the rarity of Norwalk virus infection as a cause of gastroenteritis in infants and young children in the United States. Disease outbreaks among older children and adults occur in camps, schools, nursing homes, military populations, cruise ships, and areas with contaminated drinking or swimming water. The ingestion of raw shellfish or other uncooked foods, such as salads or cake frosting, that have been handled in an unsanitary manner may lead to the disease. Outbreaks of Norwalk virus infection occur throughout the year. Other human caliciviruses appear to share the epidemiological characteristics of Norwalk virus.
Infection is transmitted by the fecal-oral route.
Although there is no conclusive evidence that the virus is also spread by the respiratory route, it could be transmitted via aerosolized virus-containing vomitus, in light of the very rapid secondary spread of infection during outbreaks. Norwalk virus may be identified in stool specimens, and antibody can be measured in serum samples by immune electron microscopic or immunoassay techniques. Viral capsid proteins, recently derived from genetically expressed cloned Norwalk virus genome, are immunogenic and may prove useful in assays to detect human antibodies. Norwalk virus RNA has recently been detected in stool samples, and PCR techniques to perfect these assays are being developed. No specific antiviral therapy is available for Norwalk or other human calicivirus gastroenteritis.