Dynamic epidemiology of acute viral hepatitis in Japan.

The epidemiology of acute viral hepatitis (AVH) is dynamic and affected by many factors including hygiene, socioeconomic status and vaccination coverage. A total of 4,302 cases of AVH were sequentially enrolled in this nationwide study between 1980 and 2008. Of the cases of AVH, acute hepatitis A (AHA) accounted for 1,583 (36.8%), acute hepatitis B (AHB) for 1,197 (27.8%), acute hepatitis C (AHC) for 359 (8.3%), and non-A, non-B and non-C (non-ABC) for 1,163 (27.0%). Between 1980 and 1995, the proportions of AHA, AHB, AHC and non-ABC were approximately 40, 25, 10 and 25%; between 1996 and 2003, they were approximately 30, 30, 10 and 30%, and this shifted to approximately 10, 40, 10 and 40% in the last 5 years. The number of AHB caused by genotype A, which is not indigenous to Japan, was 6.0% between 1991 and 1996 but has been markedly increasing since 2000, to reach 52% in 2008. Autochthonous acute hepatitis E (AHE) accounted for 10-15% of non-ABC hepatitis after 2002. The etiology of AVH in Japan has been drastically changing. A marked increase of AHB genotype A and constant occurrence of autochthonous AHE require attention, and necessary measures should be taken.