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Infectious Disease and Microbiology – Blastomycosis
Blastomycosis is an acute or chronic infection caused by Blastomyces dermatitidis, a dimorphic fungus found in soil. The organism exists as mold in the environment and converts to yeast in human tissue. The annual incidence ranges from 0.3 to 1.8 cases per 100,000 population, with up to 7.4 hospital admissions per 1 million people in endemic regions. The infection is endemic in areas near bodies of water in the southeastern United States and along the Mississippi, Ohio, and St. Lawrence River valleys. It is also found along the Mediterranean coast, in South America, Mexico, and parts of Africa. Although previously thought to affect middle-aged men more commonly, this is likely related to environmental exposure patterns rather than gender predisposition. Immunocompromised individuals are at risk for more severe disease and poorer outcomes. Prevention focuses on minimizing exposure in endemic regions, including the use of respiratory protection for individuals at occupational risk.
Infection occurs through inhalation of conidia from the environment, with potential for hematogenous dissemination to other organs. The immune system more effectively clears the conidial form; however, once inside the host, the organism converts into a broad-based budding yeast form that is less susceptible to immune clearance. Reactivation may occur in immunocompromised patients.
Clinically, blastomycosis most commonly presents as pulmonary disease. Acute pneumonia presents with fever, night sweats, productive cough, dyspnea, and pleuritic chest pain, and may be accompanied by rash. Chronic pneumonia resembles pulmonary tuberculosis, with subacute onset of fever, night sweats, weight loss, mild productive cough, and sometimes hemoptysis. Disseminated disease can involve the skin, bones, genitourinary tract, central nervous system, or other organs. Skin lesions are typically non-tender papules, nodules, or plaques that may become verrucous or ulcerated. Soft tissue swelling may occur and can form draining tracts. CNS involvement may manifest as meningitis or focal neurologic deficits.
Diagnosis relies primarily on culture and direct visualization. Serologic testing is limited due to cross-reactivity with other endemic mycoses. Urine antigen testing is available but also limited by cross-reactivity. Chest radiography may reveal masses, nodules, lobar infiltrates, or cavitary lesions; lymphadenopathy is uncommon. Culture is positive in approximately 86% of sputum samples and 92% of bronchoalveolar lavage specimens. Wet mount preparations using potassium hydroxide or calcofluor white have about 46% sensitivity. The characteristic finding is a large yeast (8–15 μm) with a single broad-based bud. Histopathology shows pyogranulomas, and fungal elements are more easily visualized with methenamine silver or periodic acid–Schiff stains. The differential diagnosis includes atypical pneumonia, lung cancer, mycobacterial disease, and squamous cell carcinoma for cutaneous lesions.
Treatment depends on severity and organ involvement. For pulmonary or disseminated non-CNS disease, amphotericin B (or a lipid/liposomal formulation) is administered for two weeks, followed by itraconazole 200 mg three times daily for three days, then 200 mg twice daily for 6–12 months. Mild to moderate disease may be treated with itraconazole alone for 6–12 months. CNS disease requires lipid/liposomal amphotericin B (3–5 mg/kg IV for 4–6 weeks), followed by at least 12 months of oral azole therapy (itraconazole, fluconazole, or voriconazole). Immunocompromised patients should receive amphotericin B followed by itraconazole for at least 12 months, and lifelong suppressive therapy may be considered. In children with mild disease, itraconazole (10 mg/kg/day) is recommended for 6–12 months; severe disease requires amphotericin followed by itraconazole. In pregnancy, amphotericin B is the treatment of choice, as azoles are contraindicated.
Patients require close monitoring for antifungal toxicity. Therapeutic drug monitoring of itraconazole is recommended after two weeks of therapy, with target levels greater than 1.0 μg/mL and less than 10 μg/mL. Liver function tests should be monitored at least every three months during azole therapy. Itraconazole should be taken with food to enhance absorption. Follow-up for approximately six months after completion of therapy is recommended due to relapse risk.
Prognosis is favorable in immunocompetent individuals, with cure rates of 90–97% when treated appropriately with amphotericin. Mortality approaches 40% in immunocompromised patients, particularly those with bone marrow transplantation or AIDS. Outcomes in pregnant women can be excellent if diagnosed early, though they are at increased risk for severe disease. Complications include respiratory failure (acute respiratory distress syndrome), CNS involvement, and relapse.
Blastomycosis is an acute or chronic infection caused by Blastomyces dermatitidis, a dimorphic fungus found in soil. The organism exists as mold in the environment and converts to yeast in human tissue. The annual incidence ranges from 0.3 to 1.8 cases per 100,000 population, with up to 7.4 hospital admissions per 1 million people in endemic regions. The infection is endemic in areas near bodies of water in the southeastern United States and along the Mississippi, Ohio, and St. Lawrence River valleys. It is also found along the Mediterranean coast, in South America, Mexico, and parts of Africa. Although previously thought to affect middle-aged men more commonly, this is likely related to environmental exposure patterns rather than gender predisposition. Immunocompromised individuals are at risk for more severe disease and poorer outcomes. Prevention focuses on minimizing exposure in endemic regions, including the use of respiratory protection for individuals at occupational risk.
Infection occurs through inhalation of conidia from the environment, with potential for hematogenous dissemination to other organs. The immune system more effectively clears the conidial form; however, once inside the host, the organism converts into a broad-based budding yeast form that is less susceptible to immune clearance. Reactivation may occur in immunocompromised patients.
Clinically, blastomycosis most commonly presents as pulmonary disease. Acute pneumonia presents with fever, night sweats, productive cough, dyspnea, and pleuritic chest pain, and may be accompanied by rash. Chronic pneumonia resembles pulmonary tuberculosis, with subacute onset of fever, night sweats, weight loss, mild productive cough, and sometimes hemoptysis. Disseminated disease can involve the skin, bones, genitourinary tract, central nervous system, or other organs. Skin lesions are typically non-tender papules, nodules, or plaques that may become verrucous or ulcerated. Soft tissue swelling may occur and can form draining tracts. CNS involvement may manifest as meningitis or focal neurologic deficits.
Diagnosis relies primarily on culture and direct visualization. Serologic testing is limited due to cross-reactivity with other endemic mycoses. Urine antigen testing is available but also limited by cross-reactivity. Chest radiography may reveal masses, nodules, lobar infiltrates, or cavitary lesions; lymphadenopathy is uncommon. Culture is positive in approximately 86% of sputum samples and 92% of bronchoalveolar lavage specimens. Wet mount preparations using potassium hydroxide or calcofluor white have about 46% sensitivity. The characteristic finding is a large yeast (8–15 μm) with a single broad-based bud. Histopathology shows pyogranulomas, and fungal elements are more easily visualized with methenamine silver or periodic acid–Schiff stains. The differential diagnosis includes atypical pneumonia, lung cancer, mycobacterial disease, and squamous cell carcinoma for cutaneous lesions.
Treatment depends on severity and organ involvement. For pulmonary or disseminated non-CNS disease, amphotericin B (or a lipid/liposomal formulation) is administered for two weeks, followed by itraconazole 200 mg three times daily for three days, then 200 mg twice daily for 6–12 months. Mild to moderate disease may be treated with itraconazole alone for 6–12 months. CNS disease requires lipid/liposomal amphotericin B (3–5 mg/kg IV for 4–6 weeks), followed by at least 12 months of oral azole therapy (itraconazole, fluconazole, or voriconazole). Immunocompromised patients should receive amphotericin B followed by itraconazole for at least 12 months, and lifelong suppressive therapy may be considered. In children with mild disease, itraconazole (10 mg/kg/day) is recommended for 6–12 months; severe disease requires amphotericin followed by itraconazole. In pregnancy, amphotericin B is the treatment of choice, as azoles are contraindicated.
Patients require close monitoring for antifungal toxicity. Therapeutic drug monitoring of itraconazole is recommended after two weeks of therapy, with target levels greater than 1.0 μg/mL and less than 10 μg/mL. Liver function tests should be monitored at least every three months during azole therapy. Itraconazole should be taken with food to enhance absorption. Follow-up for approximately six months after completion of therapy is recommended due to relapse risk.
Prognosis is favorable in immunocompetent individuals, with cure rates of 90–97% when treated appropriately with amphotericin. Mortality approaches 40% in immunocompromised patients, particularly those with bone marrow transplantation or AIDS. Outcomes in pregnant women can be excellent if diagnosed early, though they are at increased risk for severe disease. Complications include respiratory failure (acute respiratory distress syndrome), CNS involvement, and relapse.
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