Blastomycosis is caused by the dimorphic fungus Blastomyces dermatitidis that exists as a mold in the environment and as a pathogenic yeast form in the body. The reservoir is moist soil enriched with decomposing organic debris. The fungus is endemic in Ontario, Manitoba, and the south-central, south-eastern, and mid-western United States. Transmission occurs by inhalation of airborne spores after disturbance of contaminated soil.
In 2012 there were 22 reported cases of blastomycosis. This is decreased from 2011 when there were 34 cases, and is the lowest case count since 1999. The median age of cases was 52 years (range 12 to 82 years), 73% were male. Nineteen (86%) of cases were white, 1 (5%) was black, 1 (5%) was American Indian, and 1 (5%) unknown race. Fifteen (68%) cases were hospitalized, for a median of 6 days (range 1 to 21 days); 1 (5%) case died. Nineteen (86%) cases had pulmonary infections, and 3 (14%) had disseminated infections.
From 1999 to 2012, there were 445 blastomycosis cases; the median number of cases annually is 33 (range 22 to 49). From 1999 to 2012, 95 (28%; based on total number of counties where we have this information) cases were likely exposed in St. Louis County, Itasca (29 cases, 9%), Cass (16 cases, 5%), Beltrami (13 cases, 4%), Chisago (13 cases, 4%), and Washington (10 cases, 3%) Counties, which are known to be endemic
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