Reliable differentiation of Pneumocystis pneumonia from Pneumocystis colonisation by quantification of Major Surface Glycoprotein gene using real-time polymerase chain reaction.

A clear differentiation between pneumonia due to Pneumocystis jirovecii and "colonisation" is required for optimal case management. A quantification of fungal burden using major surface glycoprotein (MSG) gene-based real-time PCR was undertaken for the same. Lower respiratory tract samples collected from 104 patients of clinically suspected Pneumocystis pneumonia (PCP) were subjected to quantitative PCR using MSG gene. Based on whether or not the cases were treated for PCP, the efficacy of qPCR to differentiate between "diseased" and "colonised" was evaluated. Standard curve of plasmid-cloned gene and receiver operating characteristic curve defined a cut-off of Ct ≤ 25 to diagnose PCP and Ct within 26-39.3 range to depict colonisation. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the qPCR was 100%, each for diagnosing PCP. MSG-gene-based qPCR is a robust tool for the reliable differentiation of Pneumocystis pneumonia from colonisation.