Diagnostic approach to Pneumocystis carinii pneumonia in the setting of prophylactic aerosolized pentamidine.

Recurrent Pneumocystis carinii pneumonia is common in patients with the acquired immunodeficiency syndrome who receive prophylaxis with aerosolized pentamidine. In this setting, the number of organisms is reduced and the clinical presentation may be altered. These observations have led to doubts regarding the use of induced sputum to diagnose PCP in patients receiving prophylactic AP. To determine if the examination of induced sputum is useful for patients receiving prophylactic AP, we examined our results over a 12-month period. We also examined several clinical criteria to ascertain if they could predict the likelihood of a positive induced sputum. As assessed by P(A-a)O2, need for admission and mortality, patients receiving AP presented with less severe disease than those not receiving AP. Twelve of 19 (63 percent) patients who developed PCP while receiving prophylactic AP were diagnosed by induced sputum. Induced sputum was positive for 35 of 55 (64 percent) patients who developed PCP and had not been receiving AP. However, there were no clinical characteristics which predicted a positive induced sputum. We conclude that induced sputum is an effective method for diagnosing PCP in patients receiving prophylactic AP.