Health Care Provider Information on Blastomycosis
Blastomycosis is a systemic fungal infection caused by the thermally-dimorphic Blastomyces species found in soil. Infection with B. dermatitidis or B. gilchristii occurs primarily via inhalation of conidia and most often causes acute pulmonary symptoms, ranging from mild to fulminant. Direct traumatic inoculation of soft tissue occurs rarely.
In North America, blastomycosis occurs primarily in areas surrounding the Great Lakes, the Mississippi and Ohio River valleys, and the St. Lawrence River, including many states and provinces. In Minnesota, incidence is highest in northeastern counties. Many cases are resident in other areas of the state and are exposed while traveling "up north." However, exposures to blastomycosis have occurred throughout the state. (See maps page.)
Blastomyces species are associated with soil that is moist and enriched with decomposing organic material, such as wood and leaves. There are no available methods to test soil for Blastomyces, so the endemic range is determined from epidemiological data. Outbreaks of blastomycosis have been associated with excavation, construction, and outdoor recreation. Individual cases often report these as well, but not all cases have these classic exposures.
In Minnesota, 71% of cases are male, and the median age is 44 years (range 3-93). Most cases are white (83%), 7% are American Indian/Alaska Native, 5% are Black and 4% are Asian/Pacific Islander. From 1999 to 2018, the statewide average annual incidence was 0.64 cases/100,000 population. During the same time frame, the average annual incidence was highest for American Indian/Alaska Natives (2.7/100,000 population) followed by Whites (0.53/100,000), Asian/Pacific Islanders (0.51/100,000), and Blacks (0.48/100,000).
The incubation period for blastomycosis ranges from 3 weeks to 3 months. Common signs and symptoms of acute pulmonary blastomycosis are non-specific and include cough, fever, shortness of breath, night sweats, chills, fatigue, weight loss, non-healing skin lesions, chest pain, myalgia and arthralgia. Many patients are first diagnosed with bacterial pneumonia, and are often treated with many rounds of antibiotics before fungal infections are considered.
In Minnesota, 72% of cases involve only the pulmonary system, while 21% disseminate hematogenously to other locations, primarily skin or soft tissue and bones or joints, but occasionally the central nervous system. Only 7% of cases appear to be localized non-pulmonary infections.
It is estimated that 50% of infections are asymptomatic or cause mild illness that resolves without treatment.
- Fungal culture: the gold standard, but can take days to weeks to confirm result.
- Antigen detection by enzyme immunoassay: typically performed on serum or urine, but can be used for bronchoalveolar lavage (BAL) fluid or cerebrospinal fluid. Results in 1-3 days. Cross reactions with other fungal diseases can occur, but a positive result can help guide diagnosis.
- Fungal stains on cytological or histopathologic samples: typically sputum, BAL, lung biopsy or other tissue sample. Can be highly specific and have faster results than culture, but false negatives can occur.
- Antibody tests: Immunodiffusion and complement fixation tests are available but have a low sensitivity and specificity, and are often not reliable.
- PCR: available in some laboratories to confirm cultures and histopathologic samples.
Itraconazole is the most commonly used anti-fungal treatment. Amphotericin B is often used for severely ill patients. For more detailed treatment guidelines, please consult an infectious disease physician and refer to the Infectious Diseases Society of America’s Clinical Practice Guidelines for the Management of Blastomycosis
In Minnesota, the case fatality rate is 10%. Fatal cases of blastomycosis are 5 times more likely to have had a concurrent medical condition, such as diabetes or cancer, than cases who survived.
- Reporting Blastomycosis
Minnesota Rules Governing Communicable Diseases require health care providers to report confirmed or suspected cases of blastomycosis to the Minnesota Department of Health (MDH) within 1 working day. Find out what needs to be reported and which forms to use.