Validation of FPA and cELISA for the detection of antibodies to Brucella abortus in cattle sera and comparison to SAT, CFT, and iELISA.

The fluorescence polarisation assay (FPA) is a recently described test for the serological diagnosis of Brucella infection. It has many methodological advantages over older, more established tests and can be performed in a fraction of the time. To validate the FPA, serum samples from 146 confirmed (by culture) Brucella-infected cattle were tested in conjunction with serum samples from 1947 noninfected cattle. The competitive ELISA (cELISA) was validated using these positive reference samples and 1440 negative samples, while data for the indirect ELISA (iELISA) was generated from 6957 negative samples plus the positive sera. Published diagnostic specificity (DSp) data for the complement fixation test (CFT) and serum agglutination test (SAT) was used in conjunction with the test results on the positive sera to obtain diagnostic specificity plus diagnostic sensitivity (DSn). After selection of a cutoff for the FPA and cELISA, the diagnostic specificity and sensitivity total for each test were compared. The results, with 95% confidence intervals, were: FPA (195.7+/-2.79), iELISA (195.0+/-2.70), cELISA (194.9+/-3.48), CFT (191.7+/-4.45), and SAT (180.4+/-6.33). The data presented supports the use of the FPA in diagnosis of brucellosis and questions the use of the SAT and CFT for either screening or confirmatory testing.