[Seroepidemiological study of hepatitis B virus (HBV) infection in the rural community in Kenya--changing pattern of transmission model of HBV in Kenya].

The seroepidemiological study of HBV infection has been done against 9044 inhabitants in order to define a predominant transmission mode and a target population of HBV infection in Kenya. Results are as follows: 1) A total of 379 HBV carriers were identified. The prevalence of HBV carrier ranged from 4 to 9% in adults and 1 to 2% in children under 5 years of age. 2) The prevalences of HBs antigen and anti-HBc antibody in family members of carriers were 2 or 3 times higher than the other population. 3) 60 to 90% of the carrier children under 10 years old was positive for anti-HBe and 10 to 15% of the adult carrier and the pregnant carrier were found to be positive for e antigen. 4) Yearly infection ratio by horizontal route of transmission in the carrier family (1.4%) was 4 times higher than the control groups (0.3%). 5) 49% of the 96 carrier children was born to the carrier mother and in 40% the parent was negative for HBs antigen. 6) E antigen positive carrier mothers were highly infectious against their children than anti-HBe positive carrier mothers and fathers. These results suggest that HBV infection will happen more frequently within the family members of carriers either by horizontal and vertical infection. Marked reduction of carrier rate and infectivity observed in the children under 5 years of age infers that the improved way of mass immunization using disposable needles during infancy will deplete the incidence of horizontal mode of infection and that in the future mother to baby transmission appears to be the main route of HBV infection as in other developed countries.