Blastomyces dermatitidis is one of the dimorphic fungi known to cause disease primarily within certain endemic areas scattered throughout the world. The endemic regions of North America blastomycosis include the southeastern, south central, and midwestern states (especially areas bordering the Mississippi and Ohio Rivers and the Great Lakes), adjacent areas of Canada, and a small area in upper New York State and Canada that follows the St. Lawrence River. Within these areas, blastomycosis has occurred sporadically or in outbreaks. Infection is acquired via inhalation of airborne spores from disturbed contaminated soil. Although B dermatitidis is highly infectious, symptomatic disease seems to develop in less than half of those infected.