Evaluation oftheCardTestforDiagnosis of HumanBrucellosis

centrifugation agglutination test. A total of1,701 serum specimens frompersonswithvarious degrees ofpotential exposuretobrucella organisms orcross-reactive antigens were usedinthisstudy. Incomparison with standard tubeagglutination results, thecardtesthadasensitivity of95.3%anda specificity of84.1%. Thecard-test antigen was nonreactive withserum specimens fromtularemia patients andcholera vaccinees. Ourdataindicated thatthistest measures bothimmunoglobulin G andimmunoglobulin M agglutinins. Thevalue ofthecardtestinthepresumptive serological diagnosis ofclinical brucellosis in humansappearstobelow;however, thecardtest may beofvalueinserological surveystodelineate high-risk populations. Thebrucellosis cardtest wasoriginally developedforrapid screening ofanimalsera.For cattle, this testisgenerally regarded asbeing highly specific (7,9);however, someinvestigatorshavereported itssensitivity asbeing relatively low(12). ThelowpHofthecardtestwas initially reported toinhibit nonspecific agglutinins while leaving specific agglutinins unaffected (14). Conflicting reports exist ontheclass of immunoglobulin detected inbovine serabythe card-test antigen. Someinvestigators found the antigen reacted onlywithimmunoglobulin G (IgG) agglutinins (4), whereas others haveobserved reactions withbothIgGandIgMagglutinins (6,11). Useofthecardtestinthediagnosis ofhuman brucellosis hasnotbeenextensively evaluated. Buchanan etal. (3)found that 92%of38patients tested within 6monthsafter onsetwerecardtestpositive andsuggested thatthis testcould provide laboratory support fortheimmediate initiation oftreatment forsymptomatic patients. Basedonstudies of236suspected brucella infections inhumansinIran, Nicoletti andFadaiGhotbi(8)foundclose agreement between the cardtest andstandard tubeagglutination (STA) test, with55of56STA-positive seraalso positive bythecardtest. Theyrecommended widerutilization ofthecardtest indiagnosing acute brucella infections, butfelt thatfurther investigation ofthecardtest wasnecessary before usein thediagnosis ofchronic brucellosis cases. Thepurpose ofthis studywastodetermine thediagnostic valueofthecardtestinhuman brucellosis incomparison withfourotherserological tests andtoassess theclass ofagglutinins detected bythecardtest. Forthisstudy weused serumfromindividuals withvarious degrees of exposure tobrucella organisms.