Information for Healthcare Professionals About Blastomycosis

Clinical Features

Approximately 50% of people infected with blastomycosis remain asymptomatic.¹ Symptoms usually start 3 weeks to 3 months after exposure among those who become ill. The clinical presentation of blastomycosis is often non-specific; symptoms may include:^2,3

• Fever
• Cough
• Night sweats
• Myalgia
• Arthalgia
• Anorexia
• Chest pain
• Fatigue
• Skin lesions

Acute pulmonary blastomycosis is the most common form of blastomycosis and can progress to acute respiratory distress syndrome (ARDS). Some symptomatic cases will develop extrapulmonary infection, which typically manifests as cutaneous, osteoarticular, genitourinary, or central nervous system disease.⁴

Transmission

Blastomycosis is typically acquired via inhalation of airborne conidia. Primary cutaneous blastomycosis is uncommon but can result from traumatic inoculation.¹¹

Diagnosis

• Antigen detection: Enzyme immunoassay (EIA) is typically performed on urine or serum but can also be used on bronchoalveolar lavage fluid. EIA urine antigen tests may have the highest sensitivity of noninvasive tests and the quickest turnaround time. Cross-reactions can occur with histoplasmosis and other fungal diseases.
• Antibody tests: Antibody tests such as immunodiffusion (ID) and complement fixation (CF) are available but have low sensitivity and specificity. Antibody EIAs have also been developed and have better sensitivity and specificity but can be difficult to interpret. Antibody tests may be a useful adjunct diagnostic test when an antigen test is negative or when trying to differentiate blastomycosis from histoplasmosis (e.g., if done in combination with Histoplasma antibody testing).
• Culture: Culture is the gold standard for diagnosing blastomycosis. A commercially available DNA probe (AccuProbe, GenProbe Inc.) can be used to confirm. Sensitivity can be low.
• Microscopy: Microscopy is important for detection of yeast in tissue or respiratory secretions.
• Polymerase chain reaction (PCR): Blastomyces PCR can be used to confirm culture or histopathologic identification and on blood to detect disseminated disease.

Treatment

Amphotericin B is recommended for moderate to severe disease, central nervous system disease, and for people who are immunosuppressed or pregnant. Itraconazole is recommended for mild to moderate disease and step-down therapy.

should be considered for certain antifungals, like itraconazole, when treating blastomycosis. For more detailed treatment guidelines, please refer to the Infectious Diseases Society of America’s Clinical Practice Guidelines for the Management of Blastomycosis.

Risk groups

People in endemic areas, particularly those who participate in activities that expose them to soil or plant matter, are the primary risk group. A 2019 report showed that American Indian and Alaska Natives and Asians, Native Hawaiians or other Pacific Islanders had the highest incidence rates among reported cases.¹³  Immunocompromised persons may be at higher risk for developing severe forms of the disease.¹²

Etiologic agent

Blastomycosis is caused by the dimorphic fungus Blastomyces. Most blastomycosis infections in the United States are caused by B. dermatitidis or B. gilchristii. Recent infections in the western United States have been attributed to a newly described species B. helicus.^5,6

Reservoir and endemic areas

The fungus lives in the environment, most often found in soil and decaying organic matter such as wood or leaves. Endemic areas in the United States include the midwestern, south-central, and southeastern states, particularly areas surrounding the Ohio and Mississippi River valleys, the Great Lakes, the Saint Lawrence River, and the western United States.^7,8 Parts of Canada are also endemic, particularly Ontario, Saskatchewan, Quebec, and Manitoba.⁸ Autochthonous cases have also been reported from Africa⁹ and India.¹⁰

Surveillance and statistics

Blastomycosis is reportable in certain states. Check with your state, local, or territorial public health department for more information about disease reporting requirements and procedures in your area. Get blastomycosis statistics.