Lundgren B; Department of Clinical Microbiology, Statens Serum Institut, Copenhagen, Denmark.
P.carinii pneumonia (PCP) is conventionally diagnosed by detection of the organisms (which cannot be cultured) in clinical samples, primarily bronchoalveolar lavage (BAL) and induced sputum (IS) specimens using colorimetric or immunofluorescent stains. Recent studies have suggested that DNA amplification by PCR, using primers of a variety of genes, is a more sensitive method for detecting P.carinii, especially in samples with a low number of organisms. PCR appears to have a limited role in examination of BAL fluid because of the high sensitivity of conventional methods (95%). However, conventional staining of IS has a variable sensitivity (45-78%), in part because a good quality IS sample requires experienced personnel and a cooperating patient. PCR can improve the sensitivity of ID approaching 100%. Recently, PCR amplification of samples obtained from the oral cavity by gargling with isotonic saline has been reported to have a diagnostic sensitivity for PCP of 70%. This method is easy to perform in virtually all patients, including those who are severely ill and unable to undergo more complicated or invasive sampling methods. Another approach has been to evaluate serum or peripheral blood mononuclear cells by PCR. Conflicting results using this technique has been reported, with sensitivities ranging from 0 to 100%. In rare cases of disseminated P.carinii infection, PCR on blood samples may consistently show P.carinii DNA. In conclusion PCR for diagnosing PCP is a promising approach, although it's current role in routine diagnosis remains undefined. Easy sample extraction methods, reproducible results and the use of internal controls to validate the PCR are needed. PCR is more expensive and time consuming than conventional detection methods. However, higher sensitivity of PCR-based diagnostic methods may prove useful in the examination of easily obtained non invasive specimens, which are not currently used clinically because of the low diagnostic yield with conventional stains.
Keywords: AEGIS, Polymerase Chain Reaction, Sensitivity and Specificity, Sputum, Bronchoalveolar Lavage Fluid, Bronchoalveolar Lavage, Fluorescent Antibody Technique, Direct, False Positive Reactions, Staining and Labeling, Dyes, Bronchoscopy, Human, diagnosis, AIDS
