Epidemiology of Blastomycosis in a Region of High Endemicity in North Central Wisconsin

The clinical and epidemiologic features of 73 patients with laboratory-confirmed blastomycosis who were identified over an 11-year period in North Central Wisconsin are presented. Pulmonary disease was the sole manifestation in 77% of patients. More than one-half of all patients had symptoms that included fever, cough, weight loss, night sweats, and pleuritic chest pain. Virtually all were previously healthy, and most did not have an outdoor occupation. However, 82% of these patients lived or had visited within 500 m of rivers or associated waterways. The majority experienced the onset of symptoms between December and April. The estimated mean annual incidence rate of infection for Vilas County was 40.4 cases per 100,000 persons, and that for the largest city in the county was 101.3 cases per 100,000 persons. Several areas with an exceptionally high incidence of the infection were observed. We suggest that, in regions where blastomycosis is hyperendemic, clinical disease is most often pulmonary and occurs in immunocompetent individuals and that residence near an ecological focus may be a greater risk factor for acquisition of blastomycosis than is occupation.