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Blastomyces dermatitidis is endemic to the shore of lakes and rivers in Central and Southern North America.
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Infection can occur in any host but is more severe in immunocompromised patients.
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Acute respiratory distress syndrome and central nervous system involvement are the two most serious complications of blastomycosis.
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Early diagnosis of blastomycosis can be made by demonstrating distinctive yeast forms in tissue biopsy and by antigen detection using enzyme immunoassay techniques.
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Mild to moderate
Blastomycosis
Section snippets
Key points
Epidemiology
Blastomycosis is seen most frequently in the Mississippi and Ohio River valleys, Midwestern states and Canadian provinces that border the Great Lakes, and areas adjacent to the Saint Lawrence Seaway1, 7, 8, 9, 10, 11, 12, 13, 14 (Fig. 1). However, occasional cases have been reported from Florida, Colorado, Hawaii, Israel, India, Africa, and Central and South America.2, 15, 16 Within areas known to be endemic for blastomycosis, the disease occurs in certain areas much more frequently than in
Pathogenesis
B dermatitidis is a thermally dimorphic fungus that grows as a mold in the environment, as yeast in tissues, and at 35°C to 37°C in the laboratory. The environmental mold phase is typically observed in the laboratory at 25°C as white colonies that slowly turn a light brown color. The colonies consist of branching septate hyphae that produce conidia. Yeast cells are 8 to 20 μm in diameter and are characterized by a doubly thick, refractile cell wall and broad-based budding, with the daughter
Clinical manifestations
Blastomycosis causes a spectrum of illness in regard to severity and organ involvement, ranging from asymptomatic subclinical infection to widespread disseminated infection and, less commonly, fulminant pulmonary infection with ARDS. Most infected patients remain asymptomatic.26 Blastomycosis most often involves the lungs, and symptoms appear after an incubation period of 2 to 6 weeks.2, 26 Disseminated, extrapulmonary infection can affect nearly every organ but most commonly involves the skin,
Immunocompromised Patients
Blastomycosis is described in patients with human immunodeficiency virus (HIV)/AIDS, solid organ and hematopoietic cell transplant recipients, and patients who have been treated with immunosuppressive medications, including glucocorticoids, cytotoxic agents, and tumor necrosis factor (TNF)-alpha inhibitors. In one large series, only 2.7% of patients seen before 1978 were immunocompromised compared with 23.6% between 1978 and 1991.38 Subsequent reports focused on specific populations, such as
Diagnosis
The diagnosis of blastomycosis is often delayed because of a low index of suspicion. In Mississippi, a state that has a high incidence of blastomycosis, pulmonary blastomycosis was correctly diagnosed at initial presentation only 5% of the time in one study.12 If patients had both pulmonary symptoms and cutaneous lesions, the diagnosis rate increased to 64%. In nearly half of the patients, the diagnosis was made more than 30 days into their illness.12 A thorough history that includes travel to
Treatment
The Infectious Diseases Society of America’s guidelines for the treatment of blastomycosis emphasize that all patients with blastomycosis should receive antifungal therapy regardless of the clinical presentation because of the high likelihood of progression or recurrence of the infection if not treated.57 The treatment of pulmonary and disseminated blastomycosis is determined by the severity of the disease, the presence of CNS involvement, and the host immune status.
Outcomes
Overall mortality associated with blastomycosis is reported to be 4% to 6%.3 Mortality rates as high as 18% have been reported in patients with CNS blastomycosis and as high as 89% in patients with ARDS.13, 37, 65 Immunocompromising conditions, such as AIDS and solid organ transplantation, were associated with mortality rates as high as 25% to 41% in several earlier series.37, 38, 39, 40, 41 However, more recent case series report mortality rates of 45% in patients with ARDS and no deaths from
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All authors declare that they have no financial or commercial conflicts of interest.