A Cross-Sectional Serosurvey to Estimate Pertussis Incidence and Immunization Response in Healthy Population in Beijing, China

Pertussis remains a leading cause of vaccine-preventable disease in China despite a well-established child vaccine program and high Immunization coverage. Very few pertussis cases have been reported (<16 cases annually) since 1990s in Beijing. We hypothesize the incidence is much greater and conducted this cross-section serosurvey to estimate pertussis incidence by establishing anti-pertussis toxin (anti-PT) immunoglobulin(IgG) antibody sero epidemiology and to evaluate immune response following vaccination among a random sample of the Beijing healthy population.

 Methods:  In September 2012, blood samples were obtained from 2,412 healthy individuals aged from two months to 75 years. Serum anti-PT IgG antibodies were established using commercial ELISA kits.

Results: Of the 2,412 participants,12.4% demonstrated anti-PT IgG antibody; average measured titer was 15.06IU/ml. Among 533 participants who received at least three doses of DTaP, the average pertussis antibody titer and positive rates dropped from 23.56IU/ml and 26.70% (aged 0-6 months) to 9.80IU/ml and 2.60% (aged 7-12 months).The estimated incidence rate of recent infection (anti-PT IgG > 100 IU/ml) was 1,160 per 100,000 for 12 years or older participants; particularly the 20-30 and 41-50 age groups had much higher antibody level. 

Conclusions: the PT-IgG antibody warned rapidly after the last dose of vaccine leaving a large number of susceptible persons despite high coverage;. The real burden of pertussis was much greater than the reported suggesting adults potentially represents a high risk of transmitting pertussis to general population especially to infants. Improved control of pertussis may require providing vaccine to pregnant women, childcare providers, and  young migrated adults.  

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