Ekong Pius S, Sanderson Michael W, Shridhar Pragathi B, Cernicchiaro Natalia, Renter David G, Bello Nora M, Bai Jianfa, Nagaraja T G
Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, 66502, United States; Center for Outcomes Research and Epidemiology, Kansas State University, Manhattan, KS, 66502, United States.
Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, KS, 66502, United States; Center for Outcomes Research and Epidemiology, Kansas State University, Manhattan, KS, 66502, United States.
Prev Vet Med. 2018 Dec 1;161:90-99. doi: 10.1016/j.prevetmed.2018.10.012. Epub 2018 Oct 28.
Non-O157 Shiga toxin-producing Escherichia coli (non-O157 STEC, O26, O45, O103, O111, O121, and O145) are foodborne pathogens of public health importance. Culture and PCR-based methods have been developed for the detection of these serogroups in cattle feces. The objectives of this study were to evaluate diagnostic sensitivity and specificity of PCR- and culture-based methods for the detection of the six non-O157 serogroups, and to estimate their true prevalence in cattle feces, using a Bayesian latent class modeling approach that accounts for conditional dependence among the three methods. A total of 576 fecal samples collected from the floor of pens of finishing feedlot cattle during summer 2013 were used. Fecal samples, suspended in E. coli broth, were enriched and subjected to three detection methods: culture (involving immunomagnetic separation with serogroup specific beads and plating on a selective medium), conventional (cPCR), and multiplex quantitative PCR (mqPCR) assays. Samples were considered serogroup positive if the sample or the recovered isolate tested positive by PCR for an O gene of interest; neither Shiga toxin (stx) nor intimin (eae) genes were assessed. Prior information on the performance of the three methods was elicited from three subject experts. Culture was generally the least sensitive and most specific of the 3 tests across serogroups, mqPCR was generally the most sensitive test and cPCR more specific than mqPCR. Sensitivity analysis indicated that posterior inferences on test performance and prevalence were susceptible to prior specification in cases where few or no detections present in the data for selected combinations of diagnostic methods (i.e. extreme category problem). Our results characterize performance of detection methods and true prevalence of non-O157 serogroups, thus informing necessary adjustments for test bias in risk modeling.
非O157产志贺毒素大肠杆菌（非O157 STEC，血清型O26、O45、O103、O111、O121和O145）是具有公共卫生重要性的食源性病原体。已开发出基于培养和PCR的方法用于检测牛粪便中的这些血清型。本研究的目的是评估基于PCR和培养的方法检测这六种非O157血清型的诊断敏感性和特异性，并使用考虑三种方法之间条件依赖性的贝叶斯潜在类别建模方法估计它们在牛粪便中的真实流行率。使用了2013年夏季从育肥牛饲养场围栏地面采集的总共576份粪便样本。将粪便样本悬浮于大肠杆菌肉汤中进行增菌，并采用三种检测方法：培养（包括使用血清型特异性磁珠进行免疫磁分离并接种于选择性培养基上）、常规PCR（cPCR）和多重定量PCR（mqPCR）检测。如果样本或回收的分离株通过PCR检测出感兴趣的O基因呈阳性，则该样本被视为血清型阳性；未评估志贺毒素（stx）基因和紧密黏附素（eae）基因。从三位专家那里获取了关于这三种方法性能的先验信息。在所有血清型中，培养法通常是三种检测方法中敏感性最低且特异性最高的，mqPCR通常是最敏感的检测方法，而cPCR比mqPCR更具特异性。敏感性分析表明，在诊断方法的选定组合数据中检测很少或没有检测到的情况下（即极端类别问题），关于检测性能和流行率的后验推断易受先验设定的影响。我们的结果描述了检测方法的性能以及非O157血清型的真实流行率，从而为风险建模中检测偏差的必要调整提供了依据。
