A patient develops fever, shoness of breath, and appears to be quite ill. X-ray demonstrates bilateral interstitial lung infiltrates. Bronchial washings demonstrate small "hat-shape" organisms visible on silver stain within alveoli. Which predisposing condition is most likely to be present in this patient?

The disease is Pneumocystis pneumonia, which is caused by an agent now believed to be a fungus rather than a true bacteria. Pneumocystis carinii pneumonia is seen in immunocompromised patients, paicularly in those with AIDS, cancer, and in malnourished children. It can be the AIDS-defining illness. Congestive hea failure predisposes the patient to pulmonary edema. Pulmonary embolus can cause pulmonary infarction or sudden death. Rheumatoid ahritis, paicularly in miners, can cause formation of lung nodules similar to subcutaneous rheumatoid nodules. Ref: Brooks G.F. (2013). Chapter 45. Medical Mycology. In G.F. Brooks (Ed), Jawetz, Melnick, & Adelberg's Medical Microbiology, 26e.