An 66--year--old AIDS patient with pneumonia has a bronchoalveolar lavage that demonstrates small, "hat-shaped" structures in alveoli that are about the size of an erythrocyte and stain with silver stains. The microorganism involved is most likely which of the following?: (A) Blastomyces dermatitidis, (B) Mycobacterium a vium, (C) Mycobacterium tuberculosis, (D) Pneumocystis carinii
Answer is D. Pneumocystis carinii