Pertussis seroepidemiology in Taipei

Purpose: We evaluated the seroprevalence of pertussis among apparently healthy Taipei residents. Methods: From January 1992 through December 1994, we recruited subjects from a well baby clinic (children < 3 years), kindergartens, primary, and secondary schools and colleges (3-20) years), a health exam clinic (>20 years), and obstetric clinics (pregnant women). Subjects were stratified into 12 groups according to age and pregnant women were considered separately. The serum antibody titers against filamentous hemagglutinin (FHA) and pertussis toxin (PT) were measured by enzyme-linked immunosorbent assay. Results: The anti-PT and anti-FHA titers were elevated in the 4 to 6-month and 19 to 20-month age groups, coinciding with regular pertussis vaccinations. The anti-PT titers rose again in the 3 to 4-year age group, reflecting a higher prevalence of natural pertussis infection. The anti-PT titers gradually decreased among older age groups, although a peak occurred in the 11 to 15-year age group. The sequential changes in anti-FHA titers followed those of anit-PT titers in the younger age groups, but the anti-FHA titers were persistently elevated beyong 15 years of age. The antibody levels were similar in the two sexes, except that anti-PT titers were higher in males of 19 to 20 months and 21 to 30 years of age. Anti-PT titers were equivalent between neonates (0-2 months) and pregnant women, but anit-FHA titers were much lower in neonates. Conclusions: The seroprevalence patterns in this study indicate that young children, adolescents, and even adults remain at risk of pertussis, despite the current immunization program. Booster vaccinations after completion of the current four-dose immunization schedule, possibly continuing into adolescence, should be considered to block the transmission of infection.