Whooping Cough Caused by Bordetella pertussis and Bordetella parapertussis in an Immunized Population

Context.— The prevalence of Bordetella pertussis and Bordetella parapertussis infections among outpatients in an immunized population is not known. Objective.— To study the prevalence of these infections in outpatients with paroxysmal cough in Finland, where the pertussis vaccine coverage of 4 doses is 98%. Design.— Prospective cohort study. Setting.— Thirty-two health centers in southwestern Finland. Patients.— A total of 584 patients with paroxysmal cough seen at local health centers from October 1994 through March 1997 from whom nasopharyngeal swabs were collected. Main Outcome Measures.— Prevalence of positive cultures for B pertussis or B parapertussis and/or positive polymerase chain reaction (PCR) results and frequency of symptoms in those with pertussis and parapertussis. Results.— A total of 153 subjects (26.2%) had Bordetella infection by culture or PCR: 93 (60.8%) had B pertussis infection, 49 (32.0%) had B parapertussis infection, and 11 (7.2%) had both. Of these cases, 39 (25.5%) had positive cultures and 95 (62.1%) had positive PCR results for B pertussis, and 19 (12.4%) had positive cultures and 55 (35.9%) had positive PCR results for B parapertussis. At the time of diagnosis, no difference was found in the frequency of symptoms between patients with B parapertussis infection and those with B pertussis infection. Bordetella parapertussis infection was as common as B pertussis infection in children before school entry, whereas in schoolchildren and adults, B pertussis infection was more common than B parapertussis infection (P<.001). Conclusion.— Bordetella infections are common in an immunized population, and B parapertussis infections apparently are more prevalent than previously documented.