Objective: To determine the prevalence of Bordetella pertussis infection in adult patients with persistent cough.
Design: Prospective case series.
Setting: Urban university hospital emergency department.
Patients: Convenience sample of 75 patients aged 18 years or older with a cough lasting 2 weeks or longer. Serum specimens from 67 patients without respiratory complaints were used to develop reference values.
Interventions: In patients with cough, nasopharyngeal culture and direct fluorescent antibody testing for B pertussis were performed and serum samples were obtained at the first visit and 1 month later. Serum specimens were assayed for antibody to pertussis toxin (PT) and filamentous hemagglutinin (FHA).
Main outcome measures: A subject with one or more of the following was defined as having a pertussis infection: a positive B pertussis culture result, a four-fold change in PT or FHA titer, and/or a single PT or FHA titer at least 2 SDs greater than the geometric mean of the control group.
Results: No subject tested culture positive for B pertussis. Sixteen (21%) (95% confidence interval [CI], 13% to 32%) of 75 subjects met the serologic criteria for pertussis infection; for 13 (81%; 95% CI, 54% to 96%) of the 16, the criteria were met by the initial serum specimen. In contrast, the geometric mean levels of antibody to PT and FHA for the remaining 59 subjects with cough did not differ from those of the control group. Clinical symptoms and the lymphocyte count did not differentiate patients with pertussis from those without the disease.
Conclusion: Pertussis is a common cause of persistent cough in adults and should be considered in the differential diagnosis. Clinical symptoms, pertussis culture, direct fluorescent antibody testing, and lymphocytosis are of limited value in making the diagnosis.