Etiology of sporadic hepatitis B surface antigen-negative hepatitis.

We studied serologically 45 adults who had sporadic acute viral hepatitis that was hepatitis B surface antigen (HBsAg) negative. Two cases were due to hepatitis B virus, as demonstrated by the appearance of antibody to hepatitis B core antigen. In three other patients, the serologic pattern was inconclusive. Of 40 non-B cases, 20 were type A hepatitis and 20 were non-A, non-B hepatitis. Clinically, type A and non-A, non-B hepatitis were indistinguishable; one case of fulminant disease occurred in each group. The type A cases were more frequent in young adults; non-A, non-B disease predominated in women 35 years or older. Epidemiologic backgrounds were generally similar, including illicit self-injection; but four transfusion-associated cases were limited to the non-A, non-B group. We conclude that relatively few HBsG-negative cases are due to hepatitis B virus, and that hepatitis A virus and non-A, non-B viruses are both important in acute non-B disease.