Blastomycosis Information for Healthcare Professionals

Article

Oct 13, 2026

Blastomycosis is a fungal infection caused by Blastomyces dermatitidis, which live in soil and decaying organic matter. The infection is caused by inhaling the spores and is not spread from person to person.
While blastomycosis is rare in Halton Region (approximately 0.30 cases per 100,000 in 2025), health care professionals should consider blastomycosis in the differential diagnosis of patients who have travelled to, or are visiting from, Northern Ontario communities where the disease is more commonly reported.
Halton Region Public Health is sharing information about blastomycosis to support clinicians in its diagnosis and management and in response to recommendations from a coroner's inquest (external link) following a blastomycosis outbreak in the Constance Lake First Nation community.

Blastomyces are present in some areas of North America, including areas of Ontario, particularly northern regions. Individuals who participate in outdoor activities or have occupational exposure in endemic areas may be at increased risk of exposure to the fungus.
Disturbing soil during outdoor activities, as well as environmental events such as floods, can release fungal spores into the air. People can become infected by inhaling these spores, and approximately half of those infected will develop symptoms of blastomycosis.
Report suspected/confirmed cases of blastomycosis to Public Health by calling 311 or 905-825-6000.

Approximately 50% of cases are asymptomatic or mild.
Symptoms usually develop between three weeks to three months following exposure and commonly include fever, cough, extreme tiredness, night sweats, muscle aches, and joint pain.
Some people, such as those with weakened immune systems and underlying health conditions, may develop severe illness requiring hospitalization and, in some cases, the infection can lead to death.

For diagnosis of blastomycosis, submission of specimens for microscopy and culture (external link) are recommended. Blastomycosis can mimic other respiratory and disseminated infections and diseases and will not be identified through viral or bacterial testing; specific fungal testing is required for diagnosis.
Serology (external link) may aid in determining if a patient has been exposed to Blastomyces but should not be used as a stand-alone test for diagnosis.