HBs antigen subtypes among acute hepatitis patients in Japan: evidence of imported hepatitis.

HBs antigen subtypes were determined among 137 acute hepatitis patients in Japan. The distribution among the 99 male patients was 40 adr, 37 adw, one ayw, and 21 undetermined while that among the 38 female patients was 19 adr, 11 adw, and eight undetermined. The distribution among the male patients was different from that among HBs antigen carriers in Japan, suggesting that they were exposed not only to domestic HBs antigen carriers, but also to other sources. Thirty-one (29 males and two females) of the 137 patients (22.6%) were found to have been abroad at some time during the incubation period. The distribution among them was seven adr, 21 adw, and three undetermined. The majority had the same subtypes that are prevalent in the countries they visited, supporting the hypothesis that most of them had contracted the disease overseas. The remaining 106 patients had a distribution of the subtypes similar to that of domestic HBs antigen carriers. "Imported hepatitis" would be an important cause of acute type B hepatitis in Japan.