Diffuse pulmonary infiltrates in the immunocompromised host.

Diffuse pulmonary infiltrates in the immunocompromised host in the majority represent an opportunistic infection. However, in about 25 to 30%, they represent complications of an adverse drug reaction, recurrence of the underlying disease such as leukemia or lymphoma involving the lung, or an idiopathic "fibrosis," and in a small percentage are attributable to an "unrelated" process such as congestive heart failure, pulmonary emboli, community-acquired pneumonia, and so on. In 10 to 20% of the patients, two or more of these processes occur. A pulmonary process in the immunocompromised patient is almost always fatal unless the clinician intervenes with the proper diagnosis and/or effective empiric therapy.