Distribution of pertussis antibodies among different age groups in Japan.

We examined the distribution of antibody levels against pertussis toxin (PT) and filamentous hemagglutinin (FHA) among a healthy Japanese population aged from 0 to 77 years. Levels of both antibodies in 1108 serum samples collected in 1994 from nine prefectures were assayed using polystyrene ball ELISA. The ratio of individuals positive (>or=10 ELISA U/ml) for anti-PT and anti-FHA antibodies at ages ranging from 0 to 3 years increased rapidly with the increase in the population vaccinated over three times with acellular pertussis (aP) vaccine. However, the ratio of those positive for anti-PT antibody tended to decrease until 6-8 years of age and to increase again from 9 to 19 years among the vaccinated population, although the ratio of individuals positive for anti-FHA antibody remained constant at 80-100% in children and adolescents over 3 years old. Moreover, positivity for anti-PT antibody was high (>or=50 ELISA U/ml) in some serum samples collected from adolescents and young adults, suggesting recent symptomatic or asymptomatic infection with circulating Bordetella pertussis. On the other hand, 50-60% of infants below 12 months of age was below the detection limit (1.0 ELISA U/ml) for anti-PT and anti-FHA antibodies, and most early infants were not vaccinated for pertussis. Since intermittent circulation of B. pertussis remains among the Japanese population, complete vaccination with aP vaccine for all infants should be highly recommended to prevent pertussis.