QUANTITATIVE REAL-TIME PCR ASSAY FOR DIFFERENTIATION BETWEEN PNEUMOCYSTIS PNEUMONIA AND PNEUMOCYSTISCOLONIZATION

Pneumocystis jirovecii is a life threatening opportunistic pathogen among immunocompromised individuals. In the present study we evaluated the applicability of quantitative PCR (qPCR) assays for differentiation among diseased and colonized individuals with a diagnosis of PCP. A total of 355 patients were investigated with clinical suspicion of PCP, from whom 244 BALF and 111 induced sputum samples were obtained. All these specimens were subjected to microscopy using GMS staining, c-PCR assay and qPCR assay. 80 patients were found positive for PCP. The relevant clinical, microbiological and radiological information was available only for 68 patients and were further categorized into definite (n=12), probable (n=47) and colonizers (n=09) with P. jirovecii. The copy numbers, determined by qPCR assay, were significantly higher in definite PCP and probable PCP patients compared to colonizers. The AUC, sensitivity, and specificity for differentiating definite PCP from colonizers were 1.00, 100.0%, and 89.0%, respectively, at a cut-off value of 13950 copies/mL. The values for discriminating probable PCP from colonization were, 0.81, 72% and 78% respectively, at a cut-off value of 6580 copies/mL. However, the AUC, sensitivity, and specificity were 0.85, 75% and 78% respectively when colonizers were differentiated from both definite - probable PCP taken together, with a cut-off 7015 of copies/ml. Thus, there was an overlap between cut-off for probable PCP patients and colonizers. Therefore, the present study demonstrated that qPCR assay could be useful for discriminating definite PCP with colonizers, but had limitation for distinguishing between probable PCP from colonizers