Determining Pneumocystis jirovecii Colonisation from Infection Using PCR-Based Diagnostics in HIV-Negative...

Area of Science:

• Medical Diagnostics
• Infectious Diseases
• Molecular Biology

Background:

• Pneumocystis jirovecii pneumonia (PCP) is increasingly diagnosed in immunocompromised, HIV-negative individuals using sensitive PCR.
• Accurate differentiation between PCP infection and colonization is crucial for appropriate patient management.

Purpose of the Study:

• To assess the performance of an in-house quantitative PCR (qPCR) assay for Pneumocystis jirovecii.
• To optimize the interpretation of qPCR results in immunocompromised, HIV-negative patients.

Main Methods:

• Retrospective audit of 82 positive P. jirovecii qPCRs from induced sputum or BAL fluid (2012-2023).
• Exclusion of patients with HIV; categorization of cases (colonization, high-probability PCP, uncertain PCP) against a clinical gold standard.
• Analysis of qPCR values and correlation with clinico-radiological data and patient demographics.

Main Results:

• Significant differences in qPCR values were observed across clinical categories (infection vs. colonization).
• A cutoff of 2.5 × 10^5 copies/mL yielded 50% sensitivity and 83.33% specificity.
• A Youden Index cutoff of 6.5 × 10^4 copies/mL improved sensitivity to 75% but reduced specificity to 66.67%.
• Factors like age >70, fever, hypoxia, and ground glass changes were associated with infection.

Conclusions:

• A single qPCR cutoff is insufficient to reliably differentiate P. jirovecii infection from colonization.
• Both low and high qPCR cutoffs are useful, but a significant 'possible infection' group requires clinical and radiological interpretation.
• Standardization and prospective validation of assays in specific immunocompromised groups are needed for generalizability.