Intrafamilial cluster of hepatitis B virus infection: study of a large family in the United States.

Seventy-eight persons in an Italian-American family were tested for hepatitis B serologic markers. Fifty-one (65%) had serologic evidence of active or prior hepatitis B infection. Twenty-eight (36%) had evidence of active infection, including twenty-six with hepatitis B surface antigen (HBsAg), and two with antibody to the hepatitis B core antigen only. Severe chronic liver disease was documented in four family members, three of whom had serologic evidence of active hepatitis B infection and the fourth died before the availability of hepatitis B testing. Thirteen of 18 (72%) offspring of six HBsAg positive mothers were HBsAg positive. No epidemiologic explanation of the high prevalence of hepatitis B infection in this family was found, although mother-to-child transmission in years past is a possible explanation.