A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 29-year-old man presents to the clinic with a 4-week history of progressively worsening cough and weight loss. He recently returned from a hiking trip in Arizona. His temperature is 38.3°C (100.9°F), pulse is 100/min, respirations are 20/min, and blood pressure is 110/70 mmHg. Chest X-ray shows a right upper lobe cavitary lesion. Sputum culture grows spherules with endospores. Which of the following is the most likely causative organism?
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A
Paracoccidioides brasiliensisIncorrect. Paracoccidioides is endemic to South America and produces mariner's wheel yeast, not spherules.
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B
Cryptococcus neoformansIncorrect. Cryptococcus is an encapsulated yeast lacking spherules; it causes meningitis rather than cavitary pulmonary disease.
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C
Blastomyces dermatitidisIncorrect. Blastomyces is endemic to the Mississippi/Ohio valleys and produces broad-based budding yeast, not spherules.
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D
Histoplasma capsulatumIncorrect. Histoplasma forms small intracellular yeasts in macrophages, not spherules with endospores.
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E
Coccidioides immitisCorrect. Spherules with endospores in a patient from Arizona pathognomonically identify Coccidioides immitis.
↑ Tap an answer to reveal the reasoning
Answer: E. The patient's travel history to Arizona and the presence of spherules with endospores in the sputum indicate coccidioidomycosis. Coccidioides immitis is endemic to the Southwestern United States and forms spherules in tissues, distinguishing it from other mycoses. Histoplasma and Blastomyces show different morphologies, and Paracoccidioides is not found in the U.S.