A modified indirect fluorescent antibody test for the diagnosis of brucellosis.

We adapted the conventional indirect fluorescent antibody (IFA) test to assay IgM and IgG Brucella-specific antibodies to differentiate acute from chronic infections rather than measure total antihuman globulin specific antibodies. The results were compared with the slide agglutination test (SAT) used for screening and the quantitative microagglutination test (MAT). Of a total of 118 randomly selected samples sent for anti-Brucella antibodies received at a general hospital laboratory, 58 (47.9%) were found to be positive for IFA-IgG test but not necessarily by other tests. Eleven of these cases were positive for Brucella melitensis by culture. Sixty serum samples found negative for Brucella antibodies by IFA and other tests were of patients with medical conditions other than brucellosis. Fifty serum samples from healthy blood donors were negative for Brucella spp. antibodies by all the three tests. The IFA test was found to be a more sensitive test than MAT and distinguished an acute infection from chronic disease.