Hepatitis A virus infection: new insights from seroepidemiologic studies.

The prevalence of exposure to hepatitis A virus (HAV) increases with increasing age; decreases with increasing socioeconomic class; increases with increasing serologic evidence of prior hepatitis B virus (HBV) exposure but is much more common than HBV exposure; is independent of sex and race; varies in different parts of the world as a function of hygienic, developmental, and unrecognized geographic factors; and is not affected by immune deficiency or immaturity. Transmission of type A hepatitis is enhanced by poor personal hygiene such as that seen in institutions for the mentally retarded. On the other hand, there is no increased exposure to HAV among homosexuals, who have frequent and intimate contact with multiple sexual partners; among hemodialysis patients and staff; or among multiply transfused individuals, all of whom are at significantly increased risk of exposure to HBV. No epidemiologic evidence has confirmed the existence of viremic or intestinal carriers of HAV, and the virus is rarely, if ever, spread by parenteral mechanisms. Finally, HAV appears to play no role in chronic liver disease and a very minor role in fulminant hepatitis; however, HAV is responsible for a sizable proportion (approximately 20%--40%) of sporadic hepatitis among urban adults.