Epidemiology and mode of transmission of viral hepatitis A and B.

Viral hepatitis is now subdivided into three forms: hepatitis A (HA), epidemic or short-incubation-period hepatitis; hepatitis B (HB), homologous serum or posttransfusion hepatitis; and a third form, for which the term "hepatitis C" (HC) or "non-A-non-B hepatitis" has been proposed. Hepatitis A is usually transmitted by the anal-oral route and occurs endemically and epidemically; hepatitis B is transmitted by direct inoculation but probably almost as frequently by nonparenteral routes and is usually endemic; hepatitis C occurs after transfusion and may account for more cases of posttransfusion hepatitis than HA and HB together. Both HA and HB can be diagnosed accurately by their respective antigens and corresponding antibodies; in contrast, little is known yet about the characteristics of HC.