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Objective: To describe a large communitywide pertussis outbreak where aggressive diagnostic and treatment measures were used to control the outbreak., Design: Retrospective analysis, May 2003 through February 2004., Setting: Fond du Lac County, Wisconsin (population 98,882)., Participants: Health department personnel conducted case and contact investigations of suspected outbreak-associated illnesses using standard pertussis reporting forms and clinical evaluation and management protocols. Persons with compatible illness were tested for Bordetella pertussis using culture and for B pertussis DNA using polymerase chain reaction. Cases were classified using Council of State and Territorial Epidemiologists definitions., Interventions: Health alerts and aggressive testing and treatment of suspected cases of pertussis illness and contact prophylaxis in the community., Main Outcome Measures: Incidences by age, onsets over time, and vaccine coverage in case patients., Results: We identified 261 pertussis cases among county residents; 149 (57%) were laboratory confirmed. Of the first 57 case patients, 47% reported using a particular high school weight room. Pertussis incidence was high in all age groups; 86% of case patients were 10 years or older. Among 156 case patients with reported vaccination histories, 84% had received 5 or more doses of pertussis-containing vaccine. Adults reported significantly more severe pertussis symptoms than adolescents., Conclusions: Pertussis transmission among adolescents using a school weight room instigated a countywide outbreak with substantial incidence and morbidity among adolescents and adults. Aggressive testing and treatment in the outbreak response likely contributed to a sharp reduction in cases. This labor- and resource-intensive outbreak highlights potential benefits of pertussis booster vaccination among adolescent and adult populations.

During a large pertussis outbreak, culture and polymerase chain reaction (PCR) were used to identify 149 case patients; of these case patients, 79 had positive PCR and culture results, 59 had positive PCR results and negative culture results, 11 had negative PCR results and positive culture results (10 PCR-negative, culture-positive specimens were collected < or = 14 days after illness onset). PCR and culture of samples obtained < or = 2 weeks after illness onset and PCR of samples obtained > 2 weeks after illness onset proved to be most diagnostically useful.