[Prevalence of mutants in the determinant region of hepatitis B surface antigen among Chinese carriers after receiving only active postexposure immunoprophylaxis].
OBJECTIVE: To determine the frequency of hepatitis B surface antigen (HBsAg) mutations in the alpha determinant region among children who developed chronic hepatitis B virus (HBV) infection after receiving only active postexposure immunoprophylaxis. METHODS: HBsAg mutations were determined by PCR-directed nucleotide sequencing and sequence-specific solid-phase PCR analysis(SS-SPPCR) for 97 Chinese carrier cases after hepatitis B vaccination, for 88 children born aged women controls, and for 95 population based children controls. RESULTS: Prevalence of amino acid substitutions as detected by direct sequencing among carrier cases, women controls, and children controls were 30.9%, 10.2%, and 5.3%, respectively. The most frequent amino acid substitutions observed were at residues 145, 126, and 133. However, there was no difference in the prevalence of 145 and 126 amino acid mutants as detected by a sensitive SS-SPPCR method between carrier cases and controls. The prevalence of 145 Arg and 145 Ala mutants that were detected by SS-SPPCR was 39.2%, 33.0% and 32.6% among carrier cases, women controls, and children controls, respectively. The total odds ratio was 5.41 for mutants detected by direct sequencing. Odds ratio were 34.55 and 33.39 among adw2 subtype and genotype B subjects for mutants detected by direct sequencing, respectively. CONCLUSIONS: The results show that hepatitis B virus mutants in the determinant are fairly consistent observed but without immune selective pressures; HBV variant strains may pre-existent as minor quasispecies. The prevalence of mutants is related to HBV subtypes and genotypes.