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Although all eight genotypes of hepatitis B virus (HBV) strains are circulating in Japan, no cases of acute hepatitis with foreign HBV strains of genotype H have thus far been reported in Japan. Here, we report a 35-year-old Japanese patient with severe acute hepatitis who was domestically infected with genotype H HBV. On admission, he had a high HBV load of 1.0 x 10(9) copies/ml, elevated levels of total bilirubin (7.0 mg/dl) and alanine aminotransferase (3606 IU/l), and reduced prothrombin activity of 39.0%. The HB-JAIW05 isolate obtained in the present study was composed of 3215 nucleotides and had the highest similarity of 99.7% with the reported genotype H HBV isolate recovered from a Japanese blood donor. The HB-JAIW05 isolate had neither precore (A1896) nor core promoter (T1762/A1764) mutations. However, upon comparison with the consensus sequence of ten reported HBV isolates of the same genotype, the HB-JAIW05 isolate had 17 nucleotide substitutions including five missense mutations in the P gene, which may be related to vigorous replication of HBV in this case. He had no history of traveling abroad, but had had extramarital sexual contact with two Japanese women living in Iwate, Japan, 2 weeks and 2 months before the disease onset, respectively. Our results suggest that rare HBV genotypes such as H may be spreading in Japan via sexual contact. Further molecular epidemiological studies on HBV to clarify the exact changing profiles of de novo HBV infection in Japan in relation to genotype and genomic variability are warranted.

Hepatitis B virus (HBV) surface antigen (HBsAg) is one of the most important serological markers of current HBV infection. However, there are significant antigenic variations of HBsAg caused by genotypic diversity as well as mutation of the HBV genome. It is predictable that amino acid substitutions occurring in the HBsAg "a" determinant of a particular HBV genotype will affect the sensitivity of some diagnostic kits, since all the diagnostic kits currently available utilize monoclonal and/or polyclonal antibodies against the "a" determinant. One possible concern is that there may be a significant variation in the sensitivity of HBsAg diagnostic kits to HBsAg encoded by HBV of different genotypes, which might result in a failure to detect HBsAg of a particular HBV genotype. In this study, we assessed the reactivity of HBsAg specimens derived from three different HBV genotypes (A, B, and C) that are prevalent in Japan by 10 commercially available EIA (enzyme immunoassay), CLIA (chemiluminescent immunoassay), and CLEIA (chemiluminescent enzyme immunoassay) diagnostic kits. Specimens included both clinical samples and recombinant HBsAg. Our results showed that all the diagnostic kits evaluated were able to detect HBsAg irrespective of HBV genotypes. At the same time, it is apparent that some, but not all of the kits showed clear differences in sensitivity to the three HBV genotypes.