Infection with hepatitis B virus genotype A in Tokyo, Japan during 1976 through 2001.

Background: Because genotype A of hepatitis B virus (HBV) is not indigenous, there have been only few data on infection with it in Japan.

Methods: We examined clinical and virological features of the 66 Japanese patients who admitted Toranomon Hospital in Tokyo, Japan, between 1976 and 2001, who were found to have HBV/A infection. HBV genotype A was classified into subtype A (European type) and A' (South African type) by phylogenetic analysis of the preS1 and preS2 regions, and the S gene sequences.

Results: Of the 66 patients infected with HBV/A, 14 (21%) were asymptomatic carriers, 26 (39%) presented with acute hepatitis, 22 (33%) with chronic hepatitis, and 4 (6%) with liver cirrhosis. HBV/A infection persisted for more than 6 months in 5 of the 26 (19%) patients with acute hepatitis. The frequency of acute hepatitis in patients infected with HBV/A was higher after than before 1991 (2/22 [9%] vs 24/44 [55%]; P < 0.0001). The frequency of nucleotide 1858 of T was higher in asymptomatic carriers than in patients with acute hepatitis in whom infection was resolved (5/14 [36%] vs 0/21 [0%]; P = 0.008). Of the 57 patients for whom subtypes of genotype A were determined, subtype A was identified in 53 (93%) and subtype A' in only 4 (7%). All patients infected with subtype A' were persistently infected with HBV.

Conclusions: HBV/A infection has become more frequent during recent years, predominantly presenting as acute hepatitis, and subtype A' is uncommon in the Tokyo metropolitan area.