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.
