Frequency of illness associated with epidemic hepatitis A virus infections in adults.

Hepatitis A virus infection is often described as mild or asymptomatic, particularly in children. The failure of most adults who are found to be immune to remember symptoms of an illness suggestive of hepatitis A virus supports this belief. In 1982, two large outbreaks occurred in well documented populations of military personnel. These outbreaks were each extensively studied epidemiologically and serologically. It was found that 28/29 (96.6%) hepatitis A infections recognized prior to immune serum globulin in Outbreak A and 35/46 (76.1%) infections in Outbreak A were symptomatic. Symptomatic cases failed to occur beyond eight days of immune serum globulin administration to these predominantly susceptible groups. Between 40 and 70% of patients were icteric. Apparent contrasts in symptoms associated with hepatitis A infection in adults and children suggest a basic age-dependent difference in immune response to such infection.