The features of all known hepatitis viruses are summarized in Table 1.^10,11

Clinical features. As summarized in Table 2, parenteral transmission of HAV can occur but is relatively rare due to the short period of viremia during the illness. There is no evidence of vertical transmission from mother to baby.^5,12 Hepatitis A virus viremia is relatively brief; the incubation period is typically 15 to 60 days (mean, 30 days) after exposure, with maximal infectivity occurring prior to clinical symptoms. Treatment of HAV infection is primarily symptomatic and the disease is usually self-limiting. Severity of HAV infection can vary with age of the patient. In children hepatitis A is usually asymptomatic, whereas in adults symptomatic infection is characteristic and jaundice common.^13,14 Fulminant hepatitis A is rare and is also age-dependent, occurring more frequently in older patients.

The onset of hepatitis A is often abrupt, and characteristic prodromal symptoms of anorexia, nausea, fatigue, and others are followed, within a few days to a week, by dark urine and jaundice. Mild-to-moderate tenderness over an enlarged liver is usually detected. Serum alanine aminotransferase (ALT) and aspartate aminotransferase levels usually both rise rapidly during the prodromal period, whereas serum bilirubin concentrations reach peak levels later and decline less rapidly than serum aminotransferases. In approximately 85% of cases, the duration of jaundice persists less than 2 weeks.¹³ The majority of adults having clinically apparent disease will recover, with restoration of normal serum bilirubin and aminotransferase values within 6 months. Antibodies of the immunoglobulin (Ig)M class can be detected during the acute illness phase but decline after 6 months; during recovery IgG antibodies to HAV develop and persist indefinitely. The presence of anti-HAV IgG antibodies confers immunity to reinfection. Relapses and prolonged cholestasis are rare. Hepatitis A is an acute infection; no chronic form of HAV exists. Recovery usually occurs in 1 to 2 months.^4,5,15 The case fatality rate for HAV is 0.35% overall, but may rise to 2.5% in older adults.⁷