Application of a user-friendly Brucella-specific IgM and IgG antibody assay for the rapid confirmation of Rose Bengal-positive patients in a hospital in Iran

The Brucella IgM/IgG flow assay was used for the confirmation of brucellosis in patients from an area endemic for brucellosis and who had a Rose Bengal (RB)-positive serum sample collected at the time of first presentation for diagnosis. The flow assay confirmed the result of the RB test in 46.6% of the positive admission sera, with the majority (62.5%) of the flow assay-positive samples staining moderately strong to very strong (≥2+). In comparison, Wright and 2-ME at the routinely used cut-off titre values of 1:320 for Wright and 1:160 for 2-ME tested positive in 37.7% of the RB-positive samples. A relatively large number of RB-positive samples agglutinated at or around the cut-off value in the Wright and 2-ME tests and 66.7% of the RB-positive samples tested positive in these confirmatory tests when using one titre step lower threshold values. The relatively high number of samples with low antibody levels supports the argument for testing follow-up samples from patients with an RB-positive sample in order to confirm the diagnosis by showing seroconversion or a rise in antibody levels.