Clinical Information

Blastomyces dermatitidis, a dimorphic fungus, is endemic throughout the Midwestern, South-central, and Southeastern US, particularly in regions around the Ohio and Mississippi river valleys, the Great Lakes, and the Saint Lawrence River. It is also found in regions of Canada. Blastomyces is an environmental fungus, preferring moist soil and decomposing organic matter, which produces fungal spores that are released and inhaled by animals or humans. At body temperature, the spores mature into yeast, which can stay in the lungs or disseminate through the bloodstream to other parts of the body. Recently, through phylogenetic analysis, B dermatitidis has been separated into 2 distinct species; B dermatitidis and Blastomyces gilchristii, both able to cause blastomycosis in infected patients. Interestingly, B dermatitidis infections are associated more frequently with dissemination, particularly in older adults, individuals who smoke, and those who are immunocompromised, while B gilchristii has primarily been associated with pulmonary and constitutional symptoms.

Approximately 50% of patients infected with Blastomyces will develop symptoms, which are frequently nonspecific and include fever, cough, night sweats, myalgia or arthralgia, weight loss, chest pain and fatigue. Typically, symptoms appear anywhere from 3 weeks to 3 months following infection.

Diagnosis of blastomycosis relies on a combination of assays, including culture and molecular testing on appropriate specimens and serologic evaluation for both antibodies to and antigen released from Blastomyces. Although culture remains the gold standard method and is highly specific, the organism can take several days to weeks to grow, and sensitivity is diminished in cases of acute or localized disease. Similarly, molecular testing offers high specificity and a rapid turnaround time, however, sensitivity is imperfect. Detection of an antibody response to Blastomyces offers high specificity, however, results may be falsely negative in acutely infected patients and in patients who are immunosuppressed.