A 27-year-old man from Ohio with AIDS, chest pains, severe headaches, and a hobby of spelunking; sputum culture and spinal tap positive for a yeast-like fungus. These findings are most consistent with infection by

• A. Candida albicans.
• B. Coccidioides immitis.
• C. Cryptococcus neoformans.
• D. Histoplasma capsulatum.

Answer: (D)

Spelunking exposes you to Histoplasma capsulatum, a fungus that thrives in bat and bird droppings found in caves, a classic setting in the Ohio Valley. In people with AIDS, Histoplasma can disseminate beyond the lungs and involve the central nervous system, causing headaches, as well as pulmonary symptoms like chest pains. The finding of a yeast-like fungus in both sputum and spinal fluid fits histoplasmosis, because Histoplasma is dimorphic: it grows as a mold in the environment and as yeast in tissues and body fluids. The Ohio location plus cave exposure and the combination of pulmonary and central nervous system involvement in an immunocompromised host strongly point to Histoplasma capsulatum. Other fungi don’t fit this exposure pattern: Coccidioides is typical of southwestern deserts; Cryptococcus can cause meningitis in AIDS but isn’t linked to cave exposure; Candida is usually mucosal or bloodstream and not tied to this environmental history.