Blastomycosis in Adults

Blastomycosis is caused by inhalation of conidia of Blastomyces dermatitidis (most common) or B. gilchristii from soil rich in decaying organic matter, especially near water sources. Endemic regions include the Great Lakes basin, Mississippi-Ohio-Tennessee river valleys, southeastern United States, and parts of Manitoba and Ontario in Canada. Annual incidence ranges from 1-12 per 100,000 in endemic regions, though clinical disease is uncommon as approximately 50% of infections are asymptomatic.

Pathogenesis involves inhalation of conidia in soil dust associated with outdoor activities (hunting, camping, construction, fishing) that lodge in alveoli, convert to characteristic large yeast forms (8-15 μm with broad-based budding), and elicit pyogranulomatous inflammation. Cell-mediated immunity controls primary infection in many cases. Clinical features include asymptomatic primary infection (50%), acute pneumonia mimicking community-acquired pneumonia (lobar consolidation, fever, cough), chronic pneumonia (cavitary, fibronodular mimicking tuberculosis or malignancy), acute respiratory distress syndrome (ARDS), cutaneous involvement (most common extrapulmonary site, verrucous and ulcerative lesions), bone and joint involvement (osteomyelitis, arthritis), genitourinary disease (prostatitis, epididymitis), and CNS dissemination (chronic meningitis, brain abscesses).

Diagnosis requires direct visualization of characteristic broad-based budding yeasts in tissue (KOH preparation, calcofluor white, special stains), fungal culture (gold standard, BSL-2 to BSL-3 organism), histopathology, antigen detection in urine and serum (sensitive but cross-reacts with histoplasmosis), and serology (less reliable). Treatment depends on disease severity: itraconazole 200 mg twice daily for 6-12 months for mild-to-moderate disease, liposomal amphotericin B 3-5 mg/kg daily for severe disease, ARDS, immunocompromised hosts, or CNS involvement followed by long-term itraconazole, voriconazole or posaconazole for refractory cases or CNS disease, lifetime suppressive therapy for severely immunocompromised patients, and longer treatment durations (12+ months) for disseminated and CNS disease.