Pneumocystis pneumonia: clinical presentation and diagnosis in patients with and without acquired immune deficiency syndrome.

Pneumocystis carinii causes severe pneumonia in immunocompromised hosts. Although this most commonly occurs in patients with the acquired immunodeficiency syndrome (AIDS), other groups of immunocompromised patients without AIDS are also at risk for P. carinii pneumonia. These patients have solid or hematologic malignancies, organ transplantation, or inflammatory conditions requiring chronic immunosuppressive drugs, particularly corticosteroids. There are important differences in the clinical presentation of P. carinii pneumonia in patients with and without AIDS. P. carinii causes an acute fulminate pneumonia in patients without AIDS while patients with AIDS have more insidious involvement. The organism burden and lung inflammatory response are markedly different between these groups, contributing to substantial differences in clinical presentation, outcome, and mortality. The diagnosis of P. carinii pneumonia remains challenging for primary care physicians and specialists alike. The specific diagnosis of P. carinii pneumonia requires demonstration of the organism from a clinically relevant source, such as sputum, bronchoalveolar lavage fluid, or lung tissue. Alternative methods to diagnose P. carinii pneumonia are currently investigational and are an active area of research. The rapid and specific diagnosis of P. carinii pneumonia allows institution of specific treatment and improvement in patient outcome.