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
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.