The Brucella Reference Unit (BRU) at the University Hospital Aintree offers a national Brucella sero-diagnosis service for England, Wales, Eire and Northern Ireland. The United Kingdom is a non-endemic area with a very low prevalence of infection. The objective of this study was to evaluate new CE marked assays, Brucellacapt (Vircell) and Brucella IgG and IgM ELISAs (Vircell), against the standard set of in-house serological assays used at BRU. These include a micro-agglutination (MAG) assay, in-house IgG and IgM assays and a complement fixation test (CFT).

One hundred and forty-three archived serum samples were re-tested by both the commercial and in-house assays. Samples were divided into four distinct groups based on the most common clinical patterns of serological profiles seen (negative, clinically significant and two forms of clinical indeterminate results). The kappa test was calculated to determine the level of agreement between the commercial and in-house results.

The kappa coefficient for Brucellacapt and MAG assays was 0.90 (95% CI 0.85, 0.95) giving a very good level of agreement. Discrepancies between positive MAG and Brucellacapt assay results (5.7%) occurred only in sera with weakly reactive MAG titres of <1:160.

Similarly the kappa coefficient calculated for the IgG assays was 0.81 (95% CI 0.75, 0.87) also indicating good agreement. However, the kappa coefficient for the commercial and in-house IgM assays was poor at 0.38 (95% CI, 0.30, 0.46). The weak IgM correlation was associated in some instances, with a lack of use of IgG sorbent in the in-house assay resulting in false-negative results. In a low prevalence population, the combination of in-house and commercial immunoassays offers improvements in the sero-diagnosis of brucellosis.