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Published on: January 17, 2014
Performance of Quantitative PCR to Distinguish Pneumocystis jirovecii Pneumonia From Colonisation in
Sara Cederwall1,2,3, Erik Ottander1, David Björkhem1
1Department of Clinical Sciences Lund, Division of Infection Medicine, Lund University, Lund, Sweden.
Background:
Pneumocystis jirovecii pneumonia (PCP) is a severe opportunistic infection affecting immunocompromised patients. Quantitative polymerase chain reaction (qPCR) is widely used for the detection of P. jirovecii in respiratory samples. However, the diagnosis of PCP remains challenging and the high prevalence of P. jirovecii airway colonisation complicates the interpretation of positive results. The aim of this study was to assess the utility of P. jirovecii PCR Quantification Cycle (Cq) values in differentiating between PCP and colonisation in PCR-positive respiratory samples from immunocompromised patients.
Methods:
Adult patients with P. jirovecii detected by qPCR in respiratory samples (bronchoalveolar lavage (BAL), sputum and oral wash) collected between 2017 and 2023 were retrospectively enrolled in the study. Patients were classified as having PCP or P. jirovecii colonisation and Cq values were compared between the groups. Receiver-operating characteristics (ROC) curve analyses were used to assess the performance of Cq values to distinguish between PCP and colonisation, and to establish Cq cut-off values for the different sample types.
Result:
Of 520 included participants, 247 patients (47.5%) were classified as PCP and 273 (52.5%) as colonised. The median Cq value was significantly lower in the PCP group compared to colonised patients in BAL (33.0 vs. 36.6, p < 0.001) and sputum (33.4 vs. 36.0, p < 0.0001), yielding a ROC area under the curve of 0.75 and 0.73, respectively. Cq levels for oral wash did not differ between PCP and colonisation and lacked discriminatory power with a ROC AUC of 0.45. A Cq cut-off level at 31 for BAL and sputum could predict PCP with a positive predictive value of > 85% while Cq < 38 provided a negative predictive value of 89% for BAL and 73% for sputum.
Conclusion:
Different Cq cut-off values in BAL and sputum may support discrimination between PCP and colonisation and assist physicians in their clinical management of PCP.
Insights
Quantitative PCR (qPCR) Cq values can help distinguish Pneumocystis jirovecii pneumonia (PCP) from colonization in immunocompromised patients. Lower Cq values in bronchoalveolar lavage and sputum samples indicate PCP, aiding clinical management.
Area of Science:
- Medical Microbiology
- Infectious Diseases
- Clinical Diagnostics
Background:
- Pneumocystis jirovecii pneumonia (PCP) is a severe opportunistic infection in immunocompromised individuals.
- Quantitative polymerase chain reaction (qPCR) is used for P. jirovecii detection but differentiating PCP from colonization is challenging.
- High prevalence of P. jirovecii airway colonization complicates diagnosis and interpretation of qPCR results.
Purpose of the Study:
- To evaluate the utility of P. jirovecii PCR Quantification Cycle (Cq) values in distinguishing between PCP and colonization.
- To assess the diagnostic performance of Cq values in respiratory samples from immunocompromised patients.
- To establish Cq cut-off values for accurate PCP diagnosis.
Main Methods:
- Retrospective study of adult patients with P. jirovecii detected by qPCR in bronchoalveolar lavage (BAL), sputum, or oral wash samples (2017-2023).
- Classification of patients into PCP or P. jirovecii colonization groups based on clinical criteria.
- Comparison of Cq values between groups and receiver-operating characteristics (ROC) curve analysis to determine discriminatory power and optimal cut-off values.
Main Results:
- Of 520 patients, 247 had PCP and 273 were colonized.
- Significantly lower median Cq values were observed in PCP patients for BAL (33.0 vs. 36.6) and sputum (33.4 vs. 36.0).
- ROC analysis showed good discriminatory power for BAL (AUC=0.75) and sputum (AUC=0.73), but not for oral wash (AUC=0.45). Cq cut-offs of ≤31 for BAL/sputum predicted PCP with >85% PPV.
Conclusions:
- P. jirovecii qPCR Cq values in BAL and sputum can aid in differentiating PCP from colonization.
- Established Cq cut-off values can assist physicians in clinical management decisions for PCP.
- Oral wash Cq values lack discriminatory power for PCP diagnosis.
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