Introduction. Pneumocystis jirovecii pneumonia (PCP) is a severe disease affecting immunocompromised patients. Diagnosis is difficult due to the low sensitivity of direct examination and inability to grow the pathogen in culture. Quantitative PCR in bronchoalveolar lavage fluid (BAL) has high sensitivity, but limited specificity for distinguishing PCP from colonization.Aim. To assess the performance of an in-house quantitative PCR to discriminate between PCP and colonization.Methodology. This was a single-centre retrospective study including all patients with a positive PCR result for P. jirovecii in BAL between 2009 and 2017. Irrespective of PCR results, PCP was defined as the presence of host factors and clinical/radiological criteria consistent with PCP and (i) the presence of asci at direct examination of respiratory sample or (ii) anti-PCP treatment initiated with clinical response and absence of alternative diagnosis. Colonization was considered for cases who did not receive anti-PCP therapy with a favourable outcome or an alternative diagnosis. Cases who did not meet the above mentioned criteria were classified as 'undetermined'.Results. Seventy-one patients with positive P. jirovecii PCR were included (90 % non-HIV patients). Cases were classified as follows: 37 PCP, 22 colonization and 12 undetermined. Quantitative PCR values in BAL were significantly higher in patients with PCP versus colonization or undetermined (P<0.0001). The cut-off of 5×103 copies/ml was able to discriminate PCP cases from colonization with 97 % sensitivity, 82 % specificity, 90 % positive predictive value and 95 % negative predictive value.Conclusions. Our quantitative PCR for P. jirovecii in BAL was reliable to distinguish PCP cases from colonization in this predominantly non-HIV population.

中文翻译：

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定量PCR能够从定植中区分出吉氏肺孢子虫肺炎。

介绍。肺炎支原体肺炎（PCP）是一种严重的疾病，会影响免疫功能低下的患者。由于直接检查的敏感性低以及无法在培养物中生长病原体，因此诊断很困难。支气管肺泡灌洗液（BAL）中的定量PCR灵敏度高，但区分PCP和定植的特异性有限。评估内部定量PCR区分PCP和定植的性能。这是一项单中心回顾性研究，纳入了2009年至2017年间BAL中所有jirovecii假单胞菌PCR结果均为阳性的患者。无论PCR结果如何，PCP被定义为与PCP一致的宿主因素和临床/放射学标准的存在，以及（i）在直接检查呼吸道样本时存在asci的存在，或（ii）由临床反应开始且没有其他诊断的抗PCP治疗。对于未接受抗PCP治疗并获得良好结果或其他诊断的病例，应考虑定植。不符合上述标准的病例被分类为“不确定”。包括71例jirovecii PCR阳性的患者（90％的非HIV患者）。病例分类如下：37例PCP，22例定植和12例不确定。PCP患者的BAL中定量PCR值明显高于定植或不确定的（P <0.0001）。5×103拷贝/ ml的临界值能够以97％的敏感性，82％的特异性，90％的阳性预测值和95％的阴性预测值将PCP病例与定植区分开。我们在BAL中对jirovecii假单胞菌的定量PCR可以可靠地将PCP病例与该非HIV人群的定殖区分开。