Change in prevalent subtypes of HBsAg in acute hepatitis B infections and its implications

Subtyping of hepatitis B antigen in patients with acute hepatitis B revealed subtype ay in 75% while subtype ad was much more common in chronic asymptomatic carriers of the antigen (in 81% of blood donors). In contrast to blood donors, a change of the prevalent subtype was noted in acute hepatitis patients between 1970 and 1974. Before May 1972, subtype ad was found in 67% of patients, whereas later subtype ay dominated in 93%. An unequal distribution of subtypes between acute and chronic forms of hepatitis B infections has been explained by differences in the virulence of virus strains. Our results suggest that the higher prevalence of subtype ad was also common in acute infections. The change of the prevalent subtype in acute infections may be attributed to differences in contagion rather than differences in virulence of virus strains.