An Outbreak of Blastomycosis in North-Central Wisconsin

Blastomycosis — infection with the dimorphic fungus Blastomyces dermatitidis — is endemic in the central U.S. Most previous outbreaks have occurred in Wisconsin, where the illness is reportable and has generally been associated with outdoor activities and exposure to soil, yard waste, or waterways. In October 2009, the number of reported blastomycosis cases began to increase in Marathon County, Wisconsin. To ascertain why the increase was occurring, investigators conducted a case–control study involving the period between September 1, 2009, and June 14, 2010, as well as case–case analyses involving outbreak-period and historical cases.

Fifty-five cases of symptomatic blastomycosis were identified in 2009–2010. The patients had a median age o…