Pneumocystis jirovecii Pneumonia Diagnostic Approach: Real-Life Experience in a Tertiary Centre

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Molecular Diagnostics

Background:

• Pneumocystis jirovecii pneumonia (PJP) presents a significant mortality risk in immunocompromised individuals.
• Accurate laboratory diagnosis is crucial for effective PJP management.
• Traditional diagnostic methods like immunofluorescence assay (IFA) have limitations in sensitivity.

Purpose of the Study:

• To compare the diagnostic performance of a real-time PCR assay against IFA for PJP detection.
• To evaluate the utility of PCR across various respiratory sample types in a routine laboratory setting.

Main Methods:

• Retrospective analysis of 299 respiratory samples (bronchoalveolar lavage, tracheal aspirate, sputum) from September 2015 to April 2018.
• Comparison of real-time PCR results with IFA for *Pneumocystis jirovecii* detection.
• Calculation of sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for both assays.

Main Results:

• Real-time PCR demonstrated high sensitivity (96%) and specificity (98%) for PJP diagnosis, outperforming IFA (27% sensitivity, 100% specificity).
• PCR showed excellent PPV (90%) and NPV (99%), while IFA had 100% PPV and 87% NPV.
• Median cycle threshold (Ct) values differed significantly between definite PJP (30) and colonization (37), suggesting Ct values ≥36 can help exclude PJP.

Conclusions:

• Real-time PCR is a robust and reliable method for diagnosing PJP across all tested respiratory sample types.
• The PCR assay offers significantly improved sensitivity and specificity compared to IFA.
• Ct value analysis can further refine PJP diagnosis, with higher Ct values potentially indicating colonization rather than active infection.