Dr. Cherry's editorial [1] was a wake-up call to internists about the importance of pertussis in adults. Pertussis is "highly communicable," and immunity from available vaccines is not long lasting [2]. Outbreaks continue to occur, consuming scarce public health resources [3]. These outbreaks may be exacerbated by physicians' delays in diagnosing the disease in adults. A recent study suggests that internists' knowledge of pertussis is incomplete [4].

We investigated an outbreak of pertussis among 89 office personnel in Washington State. The index case occurred in a 31-year-old woman with paroxysms of coughing, inspiratory whoop, post-tussive vomiting, and serologic evidence of recent infection. We interviewed 61 (68.5%) of 89 employees (including the index case-patient) by using a standardized questionnaire. We defined a clinical case-patient as an employee who had had a cough illness for 2 weeks or longer and at least one of the following symptoms: inspiratory whoop, post-tussive vomiting, or paroxysmal cough. A probable case-patient was defined as an employee who had had a cough illness for at least 2 weeks that occurred during the outbreak period.

Including the index case-patient, we identified 16 case-patients (26%) (7 clinical, 9 probable) with onset within a 4-month period. An inspiratory whoop was present in 3 case-patients (19%); 12 case-patients (75%) stated that they had been vaccinated for pertussis. Although patients were tested late in their illnesses, two of three nasopharyngeal swabs collected from 3 case-patients were positive for Bordetella pertussis by polymerase chain reaction performed in the Pertussis Laboratory at the Centers for Disease Control and Prevention.

This outbreak of pertussis reaffirms the susceptibility of adults to pertussis despite a history of vaccination. We encourage physicians to consult their local public health departments for assistance with testing for B. pertussis when such diagnostic expertise is not readily available at their own medical facilities.