Pneumocystosis and quantitative PCR

•The benefit of quantitative PCR (qPCR) in respiratory secretions for diagnosing Pneumocystis pneumonia (PCP) remains uncertain. Our study included 150 patients presenting with a suspicion of PCP whose qPCR was positive. Thirty-five per cent of these patients had a positive direct examination and 14% were colonized (PCP ruled out). The median value of qPCR was significantly higher in infected patients and led to confirming the PCP diagnosis in 51 % of patients whose direct examination was negative. Pneumocystis pneumonia (PCP) is now predominantly observed in immunosuppressed non-HIV-infected patients. The sensitivity of the PCR is here higher than direct examination (DE) of respiratory secretions because the infection is caused by a lower inoculum of Pneumocystis jirovecii (P. jirovecii). The objective of our retrospective study was to assess the contribution of quantitative PCR (qPCR) in the diagnosis of PCP. All patients hospitalized for PCP suspicion with a positive qPCR were included. Irrespective of the qPCR value, patients were initially classified into two groups (infection and colonization [PCP ruled out]) based on clinical, radiological, and microbiological data. Both groups were then compared based on the qPCR value. Between 2013 and 2016, 150 patients were included; 75% of them were not infected with HIV. The diagnosis of PCP was retained for 129 patients and rejected for 21 patients. The DE was negative in 60% of PCP cases. The median value of qPCR was 76,650copies/mL among infected patients and 3220copies/mL among colonized patients. The threshold corresponding to a specificity of 100% was 56,000copies/mL. The optimal value to distinguish an infection from a colonization was 10,100copies/mL. Our study confirms the diagnostic value of the qPCR in immunosuppressed patients, especially when the DE is negative. When the qPCR is˂56,000copies/mL, the result should be interpreted based on the clinical context and paraclinical examinations. La pneumocystose pulmonaire (PCP) concerne majoritairement des patients immunodéprimés séronégatifs pour le VIH. Dans ce contexte, la sensibilité de la PCR est supérieure à l’examen direct (ED) des sécrétions respiratoires car l’infection est provoquée par une plus faible quantité de Pneumocystis jirovecii (P. jirovecii). L’objectif de notre étude rétrospective était d’évaluer l’apport de la PCR quantitative (qPCR) pour le diagnostic de PCP. Tous les patients hospitalisés pour suspicion de PCP avec une qPCR positi