Hepatitis B surface antigen: regional variation in sub-type ratio in the Canadian Red Cross donor population.

A total of 344 sera positive for hepatitis B surface antigen from volunteer blood donors at several Canadian Red Cross centres were subtyped for ad and ay specificity by counterelectrophoresis. Of the 50 sera from Toronto 21 (42%) were ad and 29 (58%) were ay; of the 95 from Montreal 82 (86%) were ad and 13 (14%) were ay; of the 199 from Quebec 179 (90%) were ad and only 20 (10%) were ay. The w and r specificities were also determined in 125 of the samples: 123 were w; the 2 samples of r specificity were from Toronto. On the other hand, among 45 sera from patients with acute hepatitis type B in Quebec 13 (29%) were ad and 33 (71%) ay.