Moodley Bhavani, Tempia Stefano, Frean John Andrew
Centre for Emerging, Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa.
Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
PLoS One. 2017 Jul 6;12(7):e0180589. doi: 10.1371/journal.pone.0180589. eCollection 2017.
Pneumocystis pneumonia (PCP) is a serious risk for HIV-positive patients. Asymptomatic infection or colonisation with P. jirovecii has been shown to occur frequently. PCR assays frequently identify such cases, due to their high sensitivity. Quantitative real-time PCR (qPCR) gene copy number cut-off values have been suggested to differentiate colonisation and infection; these need to be standardised for routine use. We compared the results of qPCR with an immunofluorescence assay (IFA) to determine a specific cut-off value.
From March 2005 through June 2009, induced sputum specimens were collected from adult patients who were clinically suspected of having PCP, at the Chris Hani Baragwanath Hospital in Gauteng, South Africa. Laboratory diagnosis of PCP was done by a conventional direct IFA and a qPCR assay. A receiver operating characteristic (ROC) analysis was performed to determine a suitable copy number cut-off value.
P. jirovecii was identified in 51% (156/305) and 67% (204/305) of specimens using IFA and qPCR, respectively. The cut-off value for the qPCR that best predicted the IFA results was 78 copies/5 μl (area under ROC curve 0.92). The sensitivity and specificity of qPCR using this cut-off was 94.6% and 89.1%, respectively, compared with the IFA.
The results of the ROC curve analysis indicate an excellent predictive value of the qPCR using the proposed cut-off. However, the IFA test is an imperfect gold standard and so this cut-off should not be used in isolation; clinical data should also contribute to the interpretation of the qPCR result.
肺孢子菌肺炎（PCP）是HIV阳性患者面临的严重风险。已表明耶氏肺孢子菌无症状感染或定植经常发生。由于其高灵敏度，PCR检测经常能识别出此类病例。已有人提出定量实时PCR（qPCR）基因拷贝数临界值来区分定植和感染；这些临界值需要标准化以便常规使用。我们将qPCR结果与免疫荧光测定法（IFA）进行比较以确定一个特定的临界值。
2005年3月至2009年6月期间，在南非豪登省克里斯·哈尼·巴拉干纳特医院，从临床怀疑患有PCP的成年患者中收集诱导痰标本。通过传统的直接IFA和qPCR检测对PCP进行实验室诊断。进行了受试者工作特征（ROC）分析以确定合适的拷贝数临界值。
分别使用IFA和qPCR在51%（156/305）和67%（204/305）的标本中鉴定出耶氏肺孢子菌。最能预测IFA结果的qPCR临界值为78拷贝/5微升（ROC曲线下面积为0.92）。与IFA相比，使用该临界值的qPCR的灵敏度和特异性分别为94.6%和89.1%。
ROC曲线分析结果表明使用所提出的临界值的qPCR具有出色的预测价值。然而，IFA检测并非完美的金标准，因此不应孤立地使用该临界值；临床数据也应有助于对qPCR结果的解读。
