Diagnosis of Midwestern Endemic Mycoses

Histoplasmosis and blastomycosis are the two most common midwestern endemic mycoses. A history of exposure to the geographic areas in which these organisms occur is central to raising suspicion for an endemic fungal infection. For infection with these organisms, the diagnosis is definitively established by recovery of the organism in tissue or body fluids, which may take weeks. A rapid diagnosis can be made by finding the distinctive yeasts in tissues or body fluids. Antigen testing allows a presumptive diagnosis of these endemic fungal infections while awaiting culture results, but cross-reactivity between assays for Histoplasma and Blastomyces is routinely seen. Antibody tests provide supportive evidence for infection with either of these endemic mycoses but are less useful in immunosuppressed patients.