A common source epidemic of North American blastomycosis

The occurrence of pulmonary blastomycosis in 4 persons in a Minnesota town (population 464), prompted an epidemiologic investigation. The search for additional cases was concentrated in the 3 families of these 4 men and another family of close friends. The investigation revealed an additional 8 probable cases among members of the 4 families; these 8 had abnormal chest X rays, but only mild or subclinical illnesses. The 4 patients with proven blastomycosis were skin tested and showed dermal hypersensitivity to blastomycin, but not to histoplasmin. Six of the 8 with probable blastomycosis reacted to blastomycin, while only 1 reacted to histoplasmin. Serologic tests for blastomycosis were positive in only 4 of the 12 patients. All 12 recovered without specific therapy. The only activity common to the 4 families was the construction of a cabin in a wooded area on a lake shore. Attempts to isolate Blastomyces dermatitidis from the environment in the vicinity of the cabin were unsuccessful.