Diemert David J, Libman Michael D, Lebel Pierre
Department of Microbiology, Montreal General Hospital, McGill University Health Centre, Montreal, Canada.
J Clin Microbiol. 2002 Nov;40(11):4056-9. doi: 10.1128/JCM.40.11.4056-4059.2002.
The COBAS AMPLICOR CT/NG test is widely used for the diagnosis of Neisseria gonorrhoeae infection using genital swabs or urine samples. Although highly specific, cross-reactivity occurs with some nonpathogenic strains of Neisseria and Lactobacillus species. In low-prevalence populations, even highly specific assays may require confirmatory testing of positive results. We assessed the positive predictive value (PPV) of this test in a low-prevalence (0.5%) setting. Genital and urine specimens testing positive using the COBAS AMPLICOR NG test were retested using an investigational 16S rRNA PCR assay. Additionally, 737 specimens were tested in parallel by both culture and the above PCR protocol. Of 9,772 specimens tested in-house, 168 were positive by the AMPLICOR test; in addition, 62 AMPLICOR-positive specimens were referred to our laboratory for confirmatory testing, yielding 230 positive specimens. Of these, 72 were confirmed positive by 16S rRNA PCR, yielding a specificity of 98.7% and a PPV of 31.3%. Specificity was similar for all specimen types, whereas PPV varied with prevalence: specimens from males, females, urine specimens, and genital swabs had PPVs of 70.8, 13.3, 51.9, and 20.1%, respectively. The PPV was higher when the initial AMPLICOR optical density (OD) was > or =3.5 versus initial and repeat OD readings in an equivocal zone of > or =0.2 to <3.5 (65.1 versus 10.1%; P < 0.001). On repeat testing of specimens with ODs in the equivocal zone, 54 gave ODs of > or =0.2 and <2.0, 35 gave ODs of > or =2.0 and <3.5, and 12 gave ODs of > or =3.5, with 3.7, 20, and 33.3% confirmed positive, respectively (P = 0.004). Comparing PCR to culture as the "gold standard," specificity increased from 96.8 to 99.9% when 16S rRNA PCR was performed on specimens positive by the COBAS AMPLICOR NG test. Confirmatory testing with a more specific method such as 16S rRNA PCR should be considered in low-prevalence populations, especially for specimens with an OD in the equivocal zone.
COBAS AMPLICOR CT/NG检测广泛用于使用生殖器拭子或尿液样本诊断淋病奈瑟菌感染。尽管该检测具有高度特异性，但仍会与一些淋病奈瑟菌非致病菌株和乳酸杆菌属发生交叉反应。在低流行率人群中，即使是高度特异性的检测也可能需要对阳性结果进行确证检测。我们在低流行率（0.5%）环境中评估了该检测的阳性预测值（PPV）。使用COBAS AMPLICOR NG检测呈阳性的生殖器和尿液标本采用一种研究性的16S rRNA PCR检测法进行重新检测。此外，737份标本同时采用培养法和上述PCR方案进行检测。在内部检测的9772份标本中，AMPLICOR检测有168份呈阳性；此外，62份AMPLICOR阳性标本被送至我们实验室进行确证检测，共有230份阳性标本。其中，72份经16S rRNA PCR确证为阳性，特异性为98.7%，PPV为31.3%。所有标本类型的特异性相似，而PPV随流行率变化：男性、女性、尿液标本和生殖器拭子标本的PPV分别为70.8%、13.3%、51.9%和20.1%。当初始AMPLICOR光密度（OD）≥3.5时的PPV高于初始和重复OD读数处于0.2至<3.5的可疑区间时的PPV（65.1%对10.1%；P<0.001）。对OD处于可疑区间的标本进行重复检测时，54份标本的OD为≥0.2且<2.0，35份标本的OD为≥2.0且<3.5，12份标本的OD为≥3.5，确证阳性率分别为3.7%、20%和33.3%（P = 0.004）。将PCR与作为“金标准”的培养法进行比较，当对COBAS AMPLICOR NG检测呈阳性的标本进行16S rRNA PCR检测时，特异性从96.8%提高到99.9%。在低流行率人群中，应考虑采用更具特异性的方法（如16S rRNA PCR）进行确证检测，尤其是对于OD处于可疑区间的标本。
