title: Estimation of receiver-operating characteristic curves to determine accuracy of a competitive enzyme-linked immunosorbent assay for the serodiagnosis of Brucella infection in domestic water buffalo (Bubalus bubalis) and cattle.
abstract: OBJECTIVE
  To estimate receiver-operating characteristic (ROC) curves for a competitive ELISA (c-ELISA) that is used in serodiagnosis of brucellosis in water buffalo and cattle, to determine the most appropriate positive cutoff value for the c-ELISA in confirmation of infection, and to evaluate species differences in c-ELISA function.
  
  
  METHODS
  Sera from 4 herds of cattle (n = 391) and 4 herds of water buffalo (381).
  
  
  METHODS
  Serum samples were evaluated for Brucella-specific antibodies by use of a c-ELISA. On the basis of previous serologic test results, iterative simulation modeling was used to classify animals as positive or negative for Brucella infection without the use of a gold standard. Accuracy of c-ELISA for diagnosis of infection was compared between cattle and water buffalo by comparison of areas under ROC curves.
  
  
  RESULTS
  A positive cutoff value of 30% inhibition for c-ELISA yielded sensitivity and specificity estimates, respectively, of 83.9 and 92.6% for cattle and 91.4 and 95.4% for water buffalo. A positive cutoff value of 35% inhibition yielded sensitivity and specificity estimates, respectively, of 83.9 and 96.2% for cattle and 88.0 and 974% for water buffalo. Areas under ROC curves were 0.94 and 0.98 for cattle and water buffalo, respectively.
  
  
  CONCLUSIONS
  ROC curves can be estimated by use of iterative simulation methods to determine optimal cutoff values for diagnostic tests with quantitative outcomes. A cutoff value of 35% inhibition for the c-ELISA was found to be most appropriate for confirmation of Brucella infection in cattle and water buffalo.
authors.affiliation: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
authors.forename: Geoffrey T
authors.initials: GT
authors.lastname: Fosgate
authors.forename: Abiodun A
authors.initials: AA
authors.lastname: Adesiyun
authors.forename: David W
authors.initials: DW
authors.lastname: Hird
authors.forename: Wesley O
authors.initials: WO
authors.lastname: Johnson
authors.forename: Sharon K
authors.initials: SK
authors.lastname: Hietala
authors.forename: Gerhardt G
authors.initials: GG
authors.lastname: Schurig
authors.forename: Joseph
authors.initials: J
authors.lastname: Ryan
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D002003:Brucella abortus / Q000302:isolation & purification*; D002007:Brucellosis, Bovine / Q000097:blood / Q000382:microbiology*; D002020:Buffaloes / Q000382:microbiology*; D002417:Cattle; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000662:veterinary*; D008390:Markov Chains; D015233:Models, Statistical; D009010:Monte Carlo Method; D012372:ROC Curve; D012680:Sensitivity and Specificity; D014300:Trinidad and Tobago
chemical_list: D000907:Antibodies, Bacterial