Scripties UMCG - Rijksuniversiteit Groningen
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No quantification cycle (Cq) differentiates colonization from infection in the diagnosis of Pneumocystis jirovecii Pneumonia using the real-time PCR technique

(2018) Basazemajja, P.P. (Peter Paul)

Introduction: The real-time PCR (rt-PCR) technique has high sensitivities (97 – 99%) and specificities (94 – 90%) in the diagnosis of Pneumocystis jirovecii Pneumonia (PJP). Because colonization cannot be excluded, different Cq cut-off values have been proposed to distinguish colonization from infection. However, these are laboratory and regional specific due to the biological nature of the pathogen and the PCR target kits used in differing laboratories. This study aims to set a cut-off Cq value to distinguish colonization from infection of P. jirovecii in the province of Friesland, The Netherlands, by using the mean Cq value of immunocompetent individuals as a reference.
Methods: A retrospective study was conducted at medical microbiology laboratory Izore of BAL samples, bronchial washes, sputum and swabs from the naso- or oral pharynx sent for rt-PCR diagnosis of PJP between September 2015 and February 2018.
Results: 54 samples were PJP positive with a mean Cq value of 27.87 (SD ± 3.40). Three samples were PJP positive in the immunocompetent (reference) group with a mean Cq value of 30.36 (SD ± 4.07). There was no significant difference between type of samples and no significant difference between the mean Cq values of the immunocompetent reference group and the immune incompetent PJP positive group. (P = 0.48).
Conclusion: No Cq value can differentiate colonization from infection in the diagnosis of PJP using the rt-PCR. PJP diagnosis in Izore remains to be based on a positive rt-PCR with the associated Cq value and accompanying amplification curve as well as the symptoms and clinical findings of the patient.

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