South-to-north gradient in distribution of the r determinant of hepatitis B surface antigen in Japan.

A total of 2.305 sera positive for hepatitis B surface antigen were obtained from asymptomatic carriers throughout Japan and subtyped for the d, y, w, and r specificities by the hemagglutination inhibition method. Determinant d prevailed in Japan (d, 99.1%; y, 0.9%), and there was no regional variation in its occurrence. In sharp contrast, there was a marked variation in the distribution of the w and r determinants, forming an apparent south-to-north gradient of r. The percentage of r determinant was highest in Kyushu (92%-94%); it decreased gradually along the axis of Japan to the north and was lowest in Akita (46%), which is located at the north end of Honshu.