Background: This multicenter study was undertaken to investigate the serologic evidence of antibodies to Bordetella pertussis toxin (IgG-PT) in children and adolescents.
Methods: IgG-PT value in a single serum collected from 1616 children and adolescents was measured by enzyme-linked immunosorbent assay in the Food and Drug Administration (FDA)-units per milliliter from November 2008 to October 2009. The relationship between time since infection and IgG anti-PT levels were analyzed and the estimated age-specific incidences of infection were calculated.
Results: The sera IgG-PT geometric mean concentrations of the samples were 1.7 FDA-U/mL. The sera protective rates of all the subjects were 6.6% (95% confidential interval [CI]: 5.4%, 7.8%). The rates in the group aged 2 years was 9.2% (95% CI: 3.5%, 14.9%), which was significantly higher than in those aged ≥3 years (χ2 = 1615, P = 0.000). In the group aged ≥3 years, 4.0% (95% CI: 3.0%, 5.0%) of the individuals tested showed an IgG-PT level ≥40 FDA-U/mL, which was equivalent to an estimated incidence of B. pertussis infection of 7000 (95% CI: 5300, 8800) per 100,000 population per year in the year before serum sampling. There were 2 peaks of estimated incidence. One peak incidence of 9100 (95% CI: 4300, 14000) per 100,000 population per year was found in the population aged >6 to 8 years. Another peak was in the population of 12- to 20-year olds with the estimated incidence of 14,600 (95% CI: 9100, 20100) per 100,000 per year.
Conclusions: The levels of protective antibodies against pertussis were very low in the immunized children aged 2 to 20 years. A booster dose of immunization for older children or adolescents should be an urgent priority. Moreover, using enzyme-linked immunosorbent assay to determine the efficiency of vaccines and even to obtain the serodiagnosis would be beneficial in controlling pertussis.