Changing seroepidemiology of hepatitis A virus infection in Taiwan.

Hepatitis A antibody (anti-HAV) in serum was studied from June to October, 1984, by radioimmunoassay in 647 male and 553 female apparently healthy children under 15 years of age in Taipei City. The prevalence rate of anti-HAV was 27.0% in infants, decreased to around 1% during the preschool age, then increased and remained around 5% until 11-12 years of age, when another increase was noted, and reached 13.6% among the early teenagers. The age-specific prevalence of anti-HAV increased with age but differed in three age ranges, which reflected three apparently different calculated annual incidences. Compared with previous studies in Taipei, the results showed a significant reduction in the prevalence of anti-HAV in almost every age group from 3 to 14 years. This fact probably reflects the marked improvement of hygienic conditions and progress in health education in recent years, which reduced the exposure to HAV infection among young children. The age of primary infection in the children was older than in previous studies, and it is expected that the susceptibility of HAV will extend to early adulthood.