Significance of positive semi-quantitative PCR tests on bronchoalveolar lavage for Pneumocystis jirovecii pneumonia in HIV-negative immunocompromised ICU patients with acute respiratory failure.

contextReal-time PCR (rt-PCR) using cycle threshold (Ct) is a semi-quantitative way to assess DNA amounts, which has become broadly used to diagnose Pneumocystis jirovecii pneumonia (PJP) in non-HIV immunocompromised patients. We aimed to describe the non-HIV immunocompromised patients hospitalized in intensive care unit (ICU) for acute respiratory failure (ARF) and to evaluate the relevance of PJP rt-PCR Ct value in diagnosing PJP. Moreover, the added value of serum 1.3 ß-D-glucan (BDG) assay in this population was also assessed.

methodsAll non-HIV immunocompromised ICU patients with ARF with at least one rt-PCR performed in broncho-alveolar lavage (BAL) from 2013 to 2023 were retrospectively included. Patients with a positive RT-PCR were classified by reviewers aware of the PCR result, but blinded to Ct values, into confirmed, uncertain, or ruled-out PJP groups based on clinical presentation, imaging findings, organism identification, laboratory results, presence of alternative diagnoses, and the resolution of acute respiratory failure with or without appropriate PJP treatment. PJ rt-PCR Ct and BDG assays of each group were compared. Uncertain diagnoses were excluded from the primary analysis and successively considered as confirmed PJP or ruled-out PJP in a secondary analysis. Using the area under the curve (AUC) of the receiver operating characteristics curves, the best threshold of Ct value was defined.

resultsOut of the 481 non-HIV immunocompromised patients who underwent a PJ rt-PCR in BAL, 59 (12%) had a positive test. The results confirmed PJP for 23/59 (39%), ruled it out for 27/59 (46%), while it remained uncertain for 9/59 (15%). Rt-PCR sensitivity and specificity were respectively 100% (95% CI = [85.7-100%]) and 94% (95% CI = [91.4-95.8%]). Median Ct and BDG levels differed significantly between the confirmed, uncertain, and ruled-out groups at 25, 31, and 34 cycles; and 523, 78, and 32 pg/ml, respectively. The primary analysis identified the best Ct to categorize patients at 30, with an AUC of 0.931 (95% CI [0.850-1.0]), a sensitivity of 86% and a specificity of 89%.

conclusionsSemi-quantitative PJ PCR was accurate in diagnosing PJP in non-HIV ICU patients with acute respiratory failure (ARF), and a Ct at low cycle values was more frequent in confirmed PJP than in colonization. The optimal Ct threshold was 30. The BDG assay was especially valuable when high levels were reached.