The declining transmission of hepatitis A in Thailand.

Hepatitis A antibody was almost universal among Thai children 10-15 years ago. To assess whether transmission of hepatitis A among Thai children had declined, contemporary antibody prevalence and seroconversion rates were determined. Antibody prevalence in 1987-1988 among children in Bangkok declined since 1977 for all ages studied, most markedly among young children. Among 453 low-income urban schoolchildren, there were no seroconversions over a 10- to 12-month period (95% confidence interval [CI] for incidence, 0-0.8%). Antibody prevalence among rural children also declined between 1985 and 1989, though rates were higher than those in Bangkok. Antibody prevalence differed by community. The annual rural infection rate was 1.1% (CI, 0.8%-1.6%). The pattern of rural hepatitis A transmission was focal. Increased numbers of susceptible children in Thailand, where hepatitis A virus still circulates, sets the stage for rising rates of symptomatic disease in adults.