Hepatitis B virus infection in Thai children

We studied hepatitis B virus (HBV) transmission among 7416 Thai children fr om 145 schools in Kamphaeng Phet province, a rural part of northern Thailan d. Their age ranged from 2 to 16 years (median 9 years). Between May 1991 a nd June 1992, 61 of 2593 (2.4%) in the cohort of susceptible children acqui red anti-HBc immunoglobulin. Ferry-seven of the 148 schools had children wh o acquired anti-HBc. School seroconversion rates to anti-HBc varied from 0% to 23%. There was no correlation between percent of carriers in schools an d percent of anti-HBc acquisition. Of the 61 children who acquired anti-HBc , eight (13%) became HBsAg carriers but only two were symptomatic, for a cl inical to subclinical infection ration of 1 : 30. One of the two symptomati c children became an HBsAg carrier. Three (38%) of the eight who were persi stently antigenemic developed antibody to hepatitis B virus e antigen. Male s were 2.5 times (95% CI 1.4-4.3) more likely to acquire anti-HBc than fema les. Risk factors for acquisition of HBc in Thailand over a 9-month period were examined in a subset of 2412 susceptible children and later in a case- control study of 22 children who acquired anti-HBc and 59 age and sex-match ed controls. Risks for acquiring anti-HBc were male gender and a history of bleeding gums. In comparing this study to an earlier pilot study among 984 8 children from the same area in Thailand, the yearly antibody acquisition rate to anti-HBc among Thai children dropped from 5.7% in 1989 to 2.4% in 1 992. A random sample of children in the pilot study showed that 16% were HB sAg positive and 27% had anti-HBc at the beginning of the study 34% had mar kers for either anti-HBc or HBsAg. 12% were repeatedly positive for HBsAg a year later.