What clinical features suggest pulmonary blastomycosis in individuals, particularly those who work outdoors, have exposure to soil or water in endemic areas, or have a compromised immune system?

Clinical Features of Pulmonary Blastomycosis

Pulmonary blastomycosis presents most commonly as either acute pneumonia mimicking bacterial infection or as chronic pneumonia indistinguishable from tuberculosis, cancer, or other fungal infections, with the key clinical clue being geographic exposure to endemic areas along the Mississippi and Ohio Rivers, Great Lakes region, or St. Lawrence Seaway. 1

Epidemiologic Risk Factors

Geographic exposure is the single most important clinical clue:

• Endemic regions include southeastern and south central states bordering the Mississippi and Ohio Rivers, midwestern states and Canadian provinces bordering the Great Lakes, and areas adjacent to the St. Lawrence Seaway 1, 2
• Point-source outbreaks occur with occupational or recreational activities along streams or rivers involving exposure to moist soil enriched with decaying vegetation 1, 2
• Outdoor workers with soil or water exposure in endemic areas are at highest risk 1, 2

Clinical Presentation Patterns

Acute Pulmonary Blastomycosis

Acute disease mimics influenza or bacterial pneumonia with an incubation period of 30-45 days: 1

• Fever, cough, and constitutional symptoms that fail to respond to standard bacterial antibiotics 1
• At least 50% of infections are asymptomatic, meaning symptomatic cases represent only the tip of the iceberg 1, 2
• A subset can progress rapidly to fulminant multilobar pneumonia and ARDS, which carries very high mortality 1

Chronic Pulmonary Blastomycosis

Most diagnosed patients present with indolent chronic pneumonia: 1

• Insidious onset of cough, weight loss, fever, and night sweats over weeks to months 1
• Clinical manifestations are indistinguishable from tuberculosis, other fungal infections, and lung cancer 1
• Symptoms persist despite empiric antibiotic therapy for presumed bacterial pneumonia 1

Radiographic Patterns

Three characteristic radiographic presentations should raise suspicion: 1

• Alveolar infiltrates (most common pattern) 1
• Mass lesions that mimic bronchogenic carcinoma 1
• Fibronodular interstitial infiltrates 1
• Diffuse pulmonary infiltrates involving all four quadrants indicate severe disease with high mortality risk 1, 3

Extrapulmonary Manifestations

25-40% of patients develop extrapulmonary disease, which strongly suggests the diagnosis: 1, 2

• Cutaneous lesions are the most common extrapulmonary manifestation—look for verrucous or ulcerative skin lesions 1
• Osteoarticular involvement presents as bone pain or joint swelling 1
• Genitourinary disease can occur, particularly in males 1
• CNS involvement is uncommon but carries high morbidity 1

High-Risk Populations

Immunocompromised patients present with more severe and disseminated disease: 1

• Organ transplant recipients 1
• HIV-infected individuals 1
• Patients on chronic immunosuppressive therapy 1
• Diabetes mellitus increases risk of ICU admission 3

Critical Diagnostic Pitfalls

Diagnostic delays are common and increase morbidity and mortality: 1

• The disease is often initially misdiagnosed as bacterial pneumonia, tuberculosis, or lung cancer 1
• Failure to consider blastomycosis in patients from endemic areas who fail standard antibiotic therapy is the most common error 1
• Prior antimicrobial therapy for presumed bacterial infection is associated with worse outcomes and ICU admission 3

Key Clinical Algorithm

When evaluating pneumonia in endemic areas, suspect blastomycosis if:

1. Patient has geographic exposure to endemic regions (Great Lakes, Mississippi/Ohio River valleys) 1, 2
2. Pneumonia fails to respond to standard bacterial antibiotics 1
3. Chronic symptoms (>3 weeks) with weight loss and night sweats are present 1
4. Radiographic findings show mass lesions mimicking cancer 1
5. Concurrent skin lesions (verrucous or ulcerative) are present 1
6. Patient is immunocompromised with severe or rapidly progressive disease 1, 3

Older age and Aboriginal ethnicity are significant risk factors for death from blastomycosis. 3