Blastomycosis

Blastomycosis is a systemic fungal infection caused by the Blastomyces dermatitidis . Of the endemic systemic mycoses, it is the least common. It is endemic in the mid-western, south-central, and south-eastern areas of the United States and in areas of Canada that border the Great Lakes. Outside North America, blastomycosis has occurred most frequently in Africa.

Blastomycosis occurs in areas with prolonged exposure to soil containing high nitrogen and organic content. Its incidence is very rare in persons with HIV and other immunocompromised people who do not live in endemic areas. 

Most commonly, blastomycosis affects the lungs. It also appears, less commonly, in the form of skin or bone lesions. A blood test can detect antibodies to Blastomyces, but a definitive diagnosis is made either by isolation of the Blastomyces in culture or through direct examination of tissue. Blastomycosis can present as acute, extrapulmonary, or disseminated disease.¹ 

Drugs used to treat blastomycosis include amphotericin, itraconazole, and ketoconazole. As blastomycosis does not frequently occur in HIV-infected patients, an optimal treatment method has not been determined. 

Guidelines from the Infectious Diseases Society of America recommend that patients dually infected with HIV and blastomycosis be treated with 1.5-2.5 grams of amphotericin B. In patients without CNS involvement, consideration may be given to switching to itraconazole after receiving 1 gram of amphotericin B.²

Maintenance therapy is recommended with itraconazole, or in patients intolerant to itraconazole or with CNS involvement, fluconazole. Discontinuation of therapy is a decision that should be made in consultation with a specialist.