Changing pattern of intrafamilial transmission of hepatitis B virus in Okinawa, Japan.

To investigate the pattern of intrafamilial spread of hepatitis B virus, the authors conducted a seroepidemiologic survey of nursery school children aged 1-5 years as well as family studies of the hepatitis B surface antigen (HBsAg)-positive children found in the survey in 1980 and 1985 in the Yaeyama district of Okinawa, Japan. The data from these family studies were compared with data from the studies conducted in 1968-1980 in the same area. Although the prevalence of HBsAg was not different for 1980 (eight of 847 children, 0.9%) and 1985 (13 of 1,355 children, 1.0%), prevalence of antibody to hepatitis B core antigen was significantly higher in 1980 (3.3%) than in 1985 (1.7%). Families were divided into four groups by the HBsAg status of the parents. In 1968-1980, families in which both parents were HBsAg-negative were most prevalent (64 of 107 families, 59.8%), followed by families in which only the mother was HBsAg-positive (17 of 107 families, 15.9%). In 1980, families in which only the mother was HBsAg-positive were most prevalent (11 of 25 families, 44.0%) and became more prevalent in 1985 (nine of 12 families, 75%). These data suggest that in the area studied, hepatitis B virus infections among children have declined over a five-year period and that mother-to-child transmission may be a main route of intrafamilial transmission in recent years.