HERD: Centre for Herd-oriented Education, Research and Development, Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, DK-1870 Frederiksberg C, Copenhagen, Denmark; Infectious Diseases, Department of Animal Medicine, Faculty of Veterinary Medicine, Zagazig University, Zagazig City 44511, Sharkia Province, Egypt.
Prev Vet Med. 2013 Nov 1;112(3-4):309-17. doi: 10.1016/j.prevetmed.2013.07.021. Epub 2013 Aug 13.
Danish farmers can order a real-time PCR mastitis diagnostic test on routinely taken cow-level samples from milk recordings. Validation of its performance in comparison to conventional mastitis diagnostics under field conditions is essential for efficient control of intramammary infections (IMI) with Staphylococcus aureus (S. aureus). Therefore, the objective of this study was to estimate the sensitivity (Se) and specificity (Sp) of real-time PCR, bacterial culture (BC) and California mastitis test (CMT) for the diagnosis of the naturally occurring IMI with S. aureus in routinely collected milk samples using latent class analysis (LCA) to avoid the assumption of a perfect reference test. Using systematic random sampling, a total of 609 lactating dairy cows were selected from 6 dairy herds with bulk tank milk PCR cycle threshold (Ct) value ≤39 for S. aureus. At routine milk recordings, automatically obtained cow-level (composite) milk samples were analyzed by PCR and at the same milking, 2436 quarter milk samples were collected aseptically for BC and CMT. Results showed that 140 cows (23%) were positive for S. aureus IMI by BC while 170 cows (28%) were positive by PCR. Estimates of Se and Sp for PCR were higher than test estimates of BC and CMT. SeCMT was higher than SeBC however, SpBC was higher than SpCMT. SePCR was 91%, while SeBC was 53%, and SeCMT was 61%. SpPCR was 99%, while SpBC was 89%, and SpCMT was 65%. In conclusion, PCR has a higher performance than the conventional diagnostic tests (BC and CMT) suggesting its usefulness as a routine test for accurate diagnosis of S. aureus IMI from dairy cows at routine milk recordings. The use of LCA provided estimates of the test characteristics for two currently diagnostic tests (BC, CMT) and a novel technique (real-time PCR) for diagnosing S. aureus IMI under field conditions at routine milk recordings in Denmark.
丹麦农民可以在常规的奶牛级别的牛奶记录样本上订购实时 PCR 乳腺炎诊断测试。在田间条件下，与常规乳腺炎诊断相比，其性能的验证对于有效控制金黄色葡萄球菌（金黄色葡萄球菌）的乳腺内感染（IMI）至关重要。因此，本研究的目的是使用潜在类别分析（LCA）来避免对完美参考测试的假设，估计实时 PCR、细菌培养（BC）和加利福尼亚乳腺炎测试（CMT）对常规收集的牛奶样本中金黄色葡萄球菌自然发生的 IMI 的诊断的敏感性（Se）和特异性（Sp）。使用系统随机抽样，从 6 个乳池中选择了总共 609 头泌乳奶牛，其牛奶 PCR 循环阈值（Ct）值≤39 用于金黄色葡萄球菌。在常规的牛奶记录中，通过 PCR 分析自动获得的奶牛级（复合）牛奶样本，并且在相同的挤奶过程中，无菌采集 2436 个四分体牛奶样本进行 BC 和 CMT。结果表明，140 头奶牛（23%）通过 BC 对金黄色葡萄球菌 IMI 呈阳性，而 170 头奶牛（28%）通过 PCR 呈阳性。PCR 的 Se 和 Sp 估计值高于 BC 和 CMT 的测试估计值。SeCMT 高于 SeBC，但是 SpBC 高于 SpCMT。SePCR 为 91%，而 SeBC 为 53%，SeCMT 为 61%。SpPCR 为 99%，而 SpBC 为 89%，SpCMT 为 65%。总之，PCR 的性能高于常规诊断测试（BC 和 CMT），表明其在常规牛奶记录中准确诊断奶牛金黄色葡萄球菌 IMI 方面具有实用性。LCA 的使用提供了两种当前诊断测试（BC、CMT）和一种新型技术（实时 PCR）在丹麦常规牛奶记录下田间条件下诊断金黄色葡萄球菌 IMI 的测试特征的估计值。
