title: Receiver operating characteristic-based assessment of a serological test used to detect Johne's disease in Israeli dairy herds.
abstract: The overall accuracy of an 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 < or = 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 < or = 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.
authors.affiliation: Department of Bacteriology, Kimron Veterinary Institute, Bet Dagan 50250, Israel.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Chaffer
authors.forename: Ariel L
authors.initials: AL
authors.lastname: Rivas
authors.forename: Daniel
authors.initials: D
authors.lastname: Elad
authors.forename: Ori
authors.initials: O
authors.lastname: Koren
authors.forename: Shlomo
authors.initials: S
authors.lastname: Garazi
authors.forename: Gerardo
authors.initials: G
authors.lastname: Chowell
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Schwager
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D019540:Area Under Curve; D002417:Cattle; D002418:Cattle Diseases / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000662:veterinary*; D005243:Feces / Q000382:microbiology*; D005260:Female; D007557:Israel / Q000453:epidemiology; D016013:Likelihood Functions; D016927:Mycobacterium avium subsp. paratuberculosis / Q000276:immunology*; D010283:Paratuberculosis / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology; D011237:Predictive Value of Tests; D015995:Prevalence; D012372:ROC Curve; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012698:Serologic Tests / Q000662:veterinary
chemical_list: D000907:Antibodies, Bacterial