Clinical significance of nested polymerase chain reaction and immunofluorescence for detection of Pneumocystis carinii pneumonia

Objective To study the clinical significance, of a nested polymerase chain reaction (PCR) method compared to. immunofluorescence (IF) for detection of Pneumocystis carinii. Methods The medical records of 89 patients with 91 episodes of pneumonia we re scrutinised. retrospectively. The pneumonia episodes were divided into c ategories according to the likelihood that the patient had had clinical Pne umocystis carinii pneumonia (PCP). All respiratory tract samples from the 8 9 patients (34 bronchoalveolar lavage (BAL) and 57 sputa) were tested for P neumocystis carinii by IF and nested PCR. Results Fifteen episodes, as diagnosed by IF, were classified as true PCP ( combination of the groups with definite and probable PCP; sensitivity 60%, specificity 97%). Among the P. carinii DNA-positive episodes, detected with nested PCP,, 24 were classified as true PCP (combination of the groups wit h definite and probable PCP; sensitivity 96%, specificity 59%), since all I F-positive samples were nested PCR positive. Only one pneumonia episode cla ssified as a probable PCP, was negative with both methods, as applied to a BAL sample. Conclusions IF applied to BAL or sputum seems to be the most specific metho d for diagnosis of clinical PCP Additional clinical cases can be found by n ested PCP,, although this then gives a high risk of detecting subclinical c olonisation of P carinii.