Situation

Northwestern Health Unit’s (NWHU) catchment area has the highest rate of blastomycosis in Ontario (2020-2024 annual rate per 100,000: 16.8-49.3 in NWHU, 0.4-0.8 in the rest of Ontario). This alert is to remind local health care partners to think Blastomycosis.

Issue

Blastomycosis can mimic other respiratory illnesses, disseminated infections and diseases will not be identified through viral or bacterial testing; specific fungal testing is required for diagnosis. Blastomycosis symptoms can seem to improve and then worsen. That means other treatments may seem to work temporarily, which can delay treatment and increase the risk of negative outcomes. Untreated infection can lead to death.

Incubation ranges from 21-106 days after exposure to the fungus, with a median of 43 days. Illness ranges from self-limiting, subclinical infection to acute or chronic pneumonia or disseminated infection.

Early diagnosis and appropriate antifungal treatment are the most important mechanism for preventing morbidity and mortality related to Blastomycosis.

Requested actions

• Please continue to consider Blastomycosis infection when assessing patients in the region. 
• Health care providers who are newer to Northwestern Health Unit’s catchment area may be unfamiliar with Blastomycosis because it is so uncommon elsewhere. Please refer to our Blastomycosis Information for Health Care Providers page for more information.
• Recommended tests include:
  • Sputum sample and/or lesional material for direct visual exam by microscopy and fungal culture. Where possible, submit multiple specimens for microscopy/culture over time to increase sensitivity. A sputum specimen which is mainly saliva is not an adequate specimen for diagnosis and may lead to false negative results.
• Other testing: 
  • Serology testing is available, but the sensitivity is poor and are generally not recommended; It is not suitable for acute diagnosis or for immunocompromised patients.
  • Antigen testing: requires to be sent to the USA for processing. It is sensitive however there is considerable cross-reactivity with other fungi. It may be suitable when collection of respiratory specimens is challenging.
  • See Public Health Ontario for further information

What is Blastomycosis?

Blastomycosis is an infection caused by the dimorphic fungus Blastomyces dermatitidis or Blastomyces gilchristii. The fungus is most common in northwestern Ontario, Manitoba, along the   Great Lakes and St. Lawrence Seaway, and in parts of the U.S.A., and is rare in other areas. It lives in the environment and is most commonly found in moist soil and in decomposing matter such as wood and leaves. 

How is it acquired?

Blastomycosis is typically acquired through inhalation of airborne spores from the disrupted environment. It primarily affects the lungs but can become a systemic infection with extrapulmonary manifestations. The most common extrapulmonary site for infection is the skin (cutaneous lesions are often located on the face and distal extremities). Other common sites include bone, the genitourinary system, and the central nervous system, but any system can be affected. Primary cutaneous blastomycosis is uncommon but can result from a traumatic puncture of the skin.  

Blastomycosis is NOT contagious i.e. it is not transmissible person-to-person or from animal-to-person. Environmental sampling is primarily done for research purposes and has been mostly unsuccessful in isolating the fungus. Testing the environment is not routinely recommended. Eradicating the fungus from soil or the environment is also not an effective means of preventing blastomycosis. Not all who are exposed to B. dermatitidis or B. gilchristii even in the same location or at the same event will become infected.  Those that are immunocompromised are at increased risk of severe disease and higher mortality. In areas where Blastomyces spp. are known to be present, the risk of infection may be reduced by avoiding activities that cause disruption of the soil; this is particularly important for individuals with compromised immune systems.

Resources

• Northwestern Health Unit – Blastomycosis Information for Health Care Providers
• PHO Webinar: Blastomycosis in Ontario: Public health and clinical considerations
• Public Health Agency of Canada – Blastomycosis for health professionals
• Public Health Ontario – Blastomycosis

Contact:
Dr. Kit Young Hoon, MPH, MSc., FRCPC 
Medical Officer of Health 
Northwestern Health Unit