Hepatitis B surface antigen in the serum of infants after deliver from asymptomatic carrier mothers.

A survey of sera of 5,993 pregnant women for hepatitis B surface antigen in Tokyo revealed 139 asymptomatic carriers (2.3%), essentially the same as that of a control population of comparable age group (2.2%). None of 59 specimens of cord blood of their newborn infants was positive for HBsAg according to an immune adherence hemagglutination assay. In 11 mother-child pairs in whom follow-up was possible for more than seven months, HBsAg was detected in the sera of eight infants within the first six months, after birth, with antigenemia persisting throughout the observation period, while antigenemia was not detected in the remaining three. The subtype of HBsAg was identical for each mother-child pair. The antigen was detected in sera of two of the infants after appropriate incubation periods of 123 and 133 days, respectively, whereas in others it was detected as early as 5 and 13 days after delivery.