Frequency of Asymptomatic Bordetella pertussis Colonization in Healthy Children and Adolescents

Abstract

Bordetella pertussis, responsible for pertussis disease (whooping cough), is an important cause of vaccine preventable deaths worldwide. While the current acellular pertussis-containing vaccine (DTaP) is highly effective in preventing severe pertussis disease in infants and toddlers, DTaP may be less effective than the whole-cell vaccine (DTP) in preventing Bordetella pertussis infections, in general. Human studies suggest that 50-80% of household contacts may be colonized in association with an index case. Given the recent outbreaks of pertussis disease in our community, we sought to characterize asymptomatic B. pertussis colonization in healthy children and their families. Healthy children and family members were enrolled in a cross-sectional study during preventive care visits in one of 3 ambulatory settings: two private practice locations and one academic healthcare system clinic. Age, pertussis vaccination status (including most recent dose), close exposure to pertussis, and history of pertussis disease were captured. Nasopharyngeal (NP) swabs were collected, and PCR was used to detect B. pertussis using IS481 and PtxS1 gene targets. Additional gene targets (IS1001, flaA) were used to evaluate the presence of other Bordetella species. 500 children and adults were enrolled (Table 1). Very few participants were unvaccinated for pertussis (3%), and few had a history of pertussis disease or recent exposure (1.4%). Bands corresponding to the expected PtxS1 PCR products were observed in 145/500 samples (29%); however, all samples were negative by PCR for IS481 (B. pertussis), IS1001 (B. parapertussis, B. holmesii), and flaA (B. bronchiseptica). Therefore, given the bp size of the PtxS1 PCR products and the lack of IS481 positivity, we concluded that all samples were negative for B. pertussis. Given the sample size of 500 children, we can be 95% confident that the true burden of colonization in otherwise healthy children and adults is likely no greater than 0.6%. While baboon data suggest that colonization and transmission of B. pertussis may occur readily after B. pertussis exposure in DTaP-vaccinated animals, the frequency of asymptomatic NP colonization is low in this population. Ongoing surveillance, particularly during periods of increased disease activity, is important.