Evaluation of an immunocapture-agglutination test (Brucellacapt) for serodiagnosis of human brucellosis

We evaluated the validity and the usefulness of a new test for the diagnosi s of human brucellosis based on an immunocapture-agglutination technique. A total of 315 sera from 82 patients with a diagnosis of brucellosis, 157 se ra from patients in whom brucellosis was suspected but not confirmed, and 4 12 sera from people living in rural areas with endemic brucellosis were stu died, The seroagglutination test (SAT), Coombs anti-Brucella test, and Bruc ellacapt test were evaluated, till the initial sera from the 82 patients pr oved to be positive in Brucellacapt and Coombs tests, while only 75 (91.4%) were positive in the SAT. If a greater than or equal to1/160 diagnostic th reshold titer was defined for the Brucellacapt test, Coombs test, and SAT, the sensitivities were 95.1, 91.5, and 65.8%, respectively. Taking the same diagnostic threshold titer for the 157 sera from the unconfirmed but suspe cted patients, the specificities of the Brucellacapt, Coombs, and SAT were 81.5, 96.2, and 100%, respectively; for the 412 control sera, the specifici ties were 99.0, 99.8, and 100%. The diagnostic efficiency (area below the r eceiver operating characteristic curve) of Brucellacapt was 0.987852 (95% c onfidence interval [CI], 0.95109 to 0.99286), very similar to the diagnosti c efficiency of the Coombs test (0.97611; 95% CI, 0.94781 to 0.99146) and h igher than that of SAT (0.91013; 95% CI, 0.86649 to 0.94317), The results o f the Brucellacapt test were compared with those of the Coombs test (correl ation coefficient, 0.956; P = 0.000) and SAT (correlation coefficient, 0.86 6; P = 0.000). The study shows very good correlation between the Brucellaca pt and Coombs tests, with a high concordance between titers obtained in the two tests. Nevertheless, lower correlation and concordance were found betw een the Brucellacapt and Coombs tests when the results for titers of greate r than or equal to1/160 were compared (0.692; P = 0.000). In acute brucello sis, the Brucellacapt and Coombs tests render positive titers of greater th an or equal to1/160, When the titers are lower, they increase significantly in the following 30 days, despite the evolution of SAT titers, In contrast , Brucellacapt and Coombs titers are always high (greater than or equal to1 /640) in brucellosis with long evolution, whether SAT titers are higher or lower than 1/160.