M. OBERLE¹, C. OTIGER¹, H. FANKHAUSER¹, G. WYSS², R. ZWEIFEL³, CH. FUX², A. CONEN<sup>2

1</sup>Institut für Labormedizin, Kantonsspital Aarau, Aarau, ²Abteilung für Infektiologie und Spitalhygiene, Kantonsspital Aarau, Aarau, ³Institut für Pathologie, Kantonsspital Aarau, Aarau

Background: Pneumocystis jiroveci, an environmental fungus, causes various pulmonary infections in immunocompromised patients. Diagnosis of P. jiroveci pneumonia (PcP) includes host factors, clinical and radiological parameters as well as the detection of cysts or trophic forms in respiratory specimens by staining, DNA amplification (PCR) or a combination of them. An ambiguous clinical presentation thereby often correlates with negative staining but positive PCR, making a definitive diagnosis difficult. Here we compare microbiological tests with the presumptive clinical diagnosis and discuss the significance of quantitative PCR (qPCR).
Material/methods: Respiratory specimens were analyzed for the presence of P. jiroveci by qPCR (mt large subunit rRNA, RIDA Pneumocystis kit, rBiopharm, Germany) and Toluidine-blue staining (Toluidine). Papanicolaou-staining (Pap) was done additionally with most of the specimens. The clinical assessment included body temperature, blood pressure, respiratory rate, oxygen saturation, arterial blood gas analysis, and a chest X-ray. Data on immunosuppressive treatments and co-morbidities were collected. Treatment was initiated upon a presumptive clinical PcP diagnosis.
Results: One hundred and nineteen specimens of 104 patients were analyzed by qPCR and Toluidine; 70% were additionally analyzed by Pap. Three cases were positive with Toluidine (positivity rate 3%) and with Pap (5%); twenty-four specimens were positive with qPCR (20%; median 4100 copies/ml, 150 – 3.6x106 copies/ml). Low qPCR (< 5000 copies/ml) resulted more often to discrepancies with the clinical PcP diagnoses whereas high copy numbers (> 10’000 copies/ml) rather confirmed the clinical investigation.
Conclusions: Here we summarize analyses for PcP of more than one hundred patients and compare clinical parameters with laboratory results. qPCR had the highest sensitivity for the detection of P. jiroveci, but its suitability for PcP-diagnosis in clinical practice is controversial. Discrepancies between clinical severity and laboratory results may lead to inconclusive diagnosis; such cases are discussed in the paper.