Assessment of Brucellosis Card test in screening patients for brucellosis.

The Brucellosis Card test (Brewers' Diagnostic Kits, Hynson, Westcott and Dunning, Inc., Baltimore, Md.) was evaluated in relation to the Brucelloslide test (bioMérieux, France), the microagglutination test (MAT) and the demonstration of brucella-specific IgG, IgM and IgA in an enzyme-linked immunosorbent assay (ELISA). A total of 573 serum specimens was tested. These included sera from patients with acute brucellosis (159), chronic brucellosis (23) and patients who had been diagnosed previously as having had brucella infection (155). Control groups consisted of patients with diseases other than brucellosis (52), others with non-infectious diseases (20), and healthy individuals (164). The Card test detected 100% of the patients with acute and 61% of the patients with chronic brucellosis. The sera from the control groups were all negative. Similar results were obtained with the Brucelloslide test and the MAT. The ELISA test detected brucella-specific Ig of all classes in the serum of patients with acute brucellosis, and IgG and IgA in the serum of patients with chronic brucellosis. In the latter group, IgM was also detected in 32% of the sera. Twenty-three per cent of sera with titres of 20 by the MAT were positive on the Card test and had ELISA titres for IgM, IgG and IgA of 400. Characterization of the antibodies involved in the Card test showed that sera with IgM ELISA titres of 1600, or an IgM titres of 800 together with IgG and IgA titres greater than or equal to 200 were Card test positive. Higher IgG (greater than or equal to 1600] plus IgA (greater than or equal to 400) titres were required to produce a positive Card test in the absence of IgM or when the IgM titre was less than or equal to 200. The Card test has a potential value as a rapid screening test for humans with acute brucellosis and shows similar results to Brucelloslide and MAT tests. ELISA, however, remains the most reliable test for diagnosis of brucellosis especially in patients with chronic and complicated stages of the disease.