Receiver operating characteristic-based assessment of a serological test used to detect Johne's disease in Israeli dairy herds

Marcelo Chaffer, Ariel L. Rivas, Daniel Elad, Ori Koren, Shlomo Garazi, Gerardo Chowell, Steven J. Schwager

Research output: Contribution to journalArticle

4 Scopus citations

Abstract

The overall accuracy of ah enzyme-linked immunosorbent assay (ELISA)used to detect Johne's disease at herd level was explored in relation to an imperfect test (fecal culture) in 57 Israeli dairy herds. Receiver-operating characteristic (ROC) analysis indicated an area under the curve (AUC) that corresponded to a test accuracy of 82.0% (69.5% to 90.9%; 95% confidence), with optimized herd sensitivity and herd specificity of 70.4% and 83.3%, respectively; and predictive values of 79.2 (+) and 75.8% (-). The optimal ELISA cutoff was 3.16% (> 3.16% seropositive cows in a herd), which was associated with likelihood ratios (LR) of 4.22 (+LR) and 0.36 (-LR), and post-test probabilities of 0.79 (+) and 0.17 (-). For herds with ≤ 200 cows (n = 19 herds), the 95% confidence interval (CI) for the AUC was 0.62-0.97 and the optimal cutoff was 3.33% (HSe = 87.5, HSp = 81.8); for herds with > 200 but ≤ 270 cows (n = 19 herds), the 95% AUC CI was 0.62-0.97 and the optimal cutoff was 1.13% (HSe = 90.0, HSp = 77.78); and for herds with > 270 cows (n = 19 herds), the 95% AUC CI was 0.69-0.99 and the optimal cutoff was 0.7% (HSe = 100.0, HSp = 70.0). The AUC was not influenced by across-herd prevalence [R2 (adjusted) = 0.0, P > 0.05]. Findings may be applied to facilitate targeted sampling of herds similar to those evaluated. For instance, a test cutoff of 0.76% could be considered for "ruling disease in," while a cutoff of 3.7% could be used for "ruling disease out." Caveats that may influence this analysis are discussed.

Original languageEnglish (US)
Pages (from-to)18-26
Number of pages9
JournalCanadian Journal of Veterinary Research
Volume72
Issue number1
StatePublished - Jan 1 2008

ASJC Scopus subject areas

  • veterinary(all)

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    Chaffer, M., Rivas, A. L., Elad, D., Koren, O., Garazi, S., Chowell, G., & Schwager, S. J. (2008). Receiver operating characteristic-based assessment of a serological test used to detect Johne's disease in Israeli dairy herds. Canadian Journal of Veterinary Research, 72(1), 18-26.