Department of Veterinary Hygiene and Public Health, School of Veterinary Medicine and Animal Science, Sao Paulo State University (UNESP), Botucatu, SP, Brazil, 18618-681.
Department of Production Animal Health, Faculty of Veterinary Medicine, University of Calgary, Calgary, AB, Canada, T2N 1N4.
J Dairy Sci. 2018 Nov;101(11):10220-10229. doi: 10.3168/jds.2018-14753. Epub 2018 Aug 23.
The objectives of this study were to estimate the accuracy of Somaticell (Idexx Laboratories Inc., Westbrook, ME), California Mastitis Test (CMT), and microbiological examination of composite milk (MEC) to diagnose Streptococcus agalactiae intramammary infections (IMI), and to assess the agreement between Somaticell and CMT to detect these infections. A secondary objective was to estimate quarter- and cow-level prevalence of S. agalactiae IMI in the herds included in the study. Seven farms were included in the study. The CMT was performed and aseptic milk samples were collected from all quarters of all lactating cows. Composite milk samples were produced in the laboratory by mixing milk from all quarters of each sampled cow. The Somaticell test was performed on a subset of S. agalactiae-positive (n = 167) and S. agalactiae-negative (n = 152) quarter milk samples. Microbiological examination of quarter milk samples (MEQ) was considered the reference test for diagnosing S. agalactiae IMI. The accuracy of all tests at various thresholds was estimated using Bayesian latent class models. Apparent prevalence of S. agalactiae IMI was 15.8% (n = 184/1,164) at the quarter level (based on MEQ) and 28.5% (n = 83/291) at the cow level (based on MEC). True prevalence, as determined by Bayesian models, was 13.0% [95% credible interval (CR): 6.4-24.4%] at the quarter level, and 25.6% (95% CR: 15.3-39.5%) at the cow level. At the cow level (n = 285), sensitivity and specificity of MEC were 95.6 and 99.5%, respectively. The accuracy of Somaticell (n = 319 quarters) to identify S. agalactiae-infected quarters was 75.4, 86.4, 88.9, 89.4, and 91.0% at thresholds of 98,000, 147,000, 205,000, 244,000, and 282,000 cells/mL, respectively. The accuracy of CMT was 87.6, 90.7, 90.8, and 87.4% at thresholds of trace, 1, 2, and 3, respectively. The areas under the receiver operating characteristic curve for Somaticell and CMT were 94.5% (95% confidence interval: 91.8-97.2%) and 92.0% (88.6-95.4%), respectively. At the tested thresholds, the sensitivity of Somaticell ranged from 94.9 to 99.5% to detect S. agalactiae IMI, and specificity ranged from 48.1 to 87.1%. The sensitivity of Somaticell at the lowest threshold (69,000 cells/mL; sensitivity = 99.9%; 95% CR: 98.2-100%) was higher than that of CMT at any tested threshold. Results of this study could be used at the farm level to reduce the use of antimicrobials and reach specific goals in S. agalactiae eradication programs.
本研究的目的是评估 Somaticell（Idexx Laboratories Inc.，缅因州 Westbrook）、加利福尼亚乳房炎测试（CMT）和复合奶（MEC）微生物检查对诊断无乳链球菌（Streptococcus agalactiae）乳腺炎感染（IMI）的准确性，并评估 Somaticell 和 CMT 对这些感染的检测结果的一致性。次要目标是估计研究中包含的牛群中无乳链球菌 IMI 的季度和牛级流行率。
共有 7 个农场参与了本研究。对所有泌乳牛的所有乳区进行 CMT 检测，并采集无菌奶样。在实验室中通过混合每个采样牛的所有乳区的奶样来制备复合奶样。对 Somaticell 阳性（n = 167）和 Somaticell 阴性（n = 152）的部分乳区奶样进行 Somaticell 检测。对乳区奶样（MEQ）的微生物检查被认为是诊断无乳链球菌 IMI 的参考试验。使用贝叶斯潜在类别模型估计了各种阈值下所有检测的准确性。基于 MEQ，无乳链球菌 IMI 的季度流行率为 15.8%（n = 184/1,164），基于 MEC 的牛级流行率为 28.5%（n = 83/291）。贝叶斯模型确定的真实流行率为 13.0% [95%可信区间（CR）：6.4-24.4%]，牛级流行率为 25.6%（95% CR：15.3-39.5%）。在牛级（n = 285），MEC 的敏感性和特异性分别为 95.6%和 99.5%。Somaticell（n = 319 个乳区）在阈值为 98,000、147,000、205,000、244,000 和 282,000 细胞/ml 时，分别为 75.4%、86.4%、88.9%、89.4%和 91.0%，以识别无乳链球菌感染的乳区。CMT 的准确性在阈值为痕迹、1、2 和 3 时分别为 87.6%、90.7%、90.8%和 87.4%。Somaticell 和 CMT 的受试者工作特征曲线下面积分别为 94.5%（95%置信区间：91.8-97.2%）和 92.0%（88.6-95.4%）。在测试的阈值下，Somaticell 检测无乳链球菌 IMI 的敏感性范围为 94.9%至 99.5%，特异性范围为 48.1%至 87.1%。Somaticell 在最低阈值（69,000 细胞/ml；敏感性 = 99.9%；95% CR：98.2-100%）的敏感性高于 CMT 在任何测试阈值的敏感性。本研究的结果可用于农场层面，以减少抗生素的使用，并在无乳链球菌根除计划中达到特定目标。
