Direct fluorescent-antibody method for the diagnosis of Pneumocystis carinii pneumonitis from sputa or tracheal aspirates from humans.

A direct fluorescent antibody (DFA) method was applied to sputum or tracheal aspirate from 68 patients with clinical or radiological evidence suggesting Pneumocystis carinii pneumonitis, and to 50 control patients. P. carinii was detected by DFA in specimens from 33 of the 69 clinical cases and 3 of the 50 controls. Specimens of lung from 11 of 33 DFA-positive cases were examined histologically, and 9 were positive. Four of 35 DFA-negative cases were examined histologically, and all were negative. Sputa or tracheal aspirates from 6 patients who were positive by both DFA and histological examination were examined also by methenamine silver staining; none could be diagnosed conclusively by this method. The results indicate that the DFA method is a sensitive and dependable procedure for the laboratory diagnosis of P. carinii pneumonitis in man.