The latest seroepidemiological pattern of hepatitis A in Japan.

Age-specific prevalence of anti-hepatitis A virus antibody (anti-HAV) was surveyed with 2,708 sera collected in 1994 in various areas of Japan. By age-group analyses, we found strong association of anti-HAV antibody with higher age group. The prevalence ratios of antibody in the groups of 30-34, 35-39, 40-44, 45-49, 50-54, 55-59, 60-64 and 65 years or older were 0, 4.2, 22.0, 44.8, 57.6, 76.4, 84.5 and 91.4%, respectively. Geometric mean titers of anti-HAV antibody in the positive age groups were approximately 6,000 mIU/ml. The seropositives among older population were ascribed to the infections more than 40 years ago and the high anti-HAV titers have been maintained since that time. In Japan, people younger than 40 years of age are extremely risky to HAV infection, since 99% have no antibody. Those in forties are also risky since two-thirds of them are seronegative. In Japan, an inactivated vaccine was licensed in 1994. Vaccination may be recommended for such high-risk groups as travelers going to endemic areas, patients who have received blood product medication and child-care staffs.