Comparison of a novel immunocapture assay with standard serological methods in the diagnosis of brucellosis.

BACKGROUND

Microbiological culture methods and immunological assays currently available are technically challenging, difficult to interpret even in non-endemic areas. They are also time consuming leading to misdiagnosis, treatment delay, and severe morbidity and mortality. Therefore, the development of a simple and accurate diagnostic assay which could be performed even in small laboratories is a pressing need. This has prompted us to evaluate an assay based on the immunocapture technique in a region where brucellosis is prevalent.

METHODS

The immunocapture test was evaluated for diagnostic efficacy on 211 patients with suspected brucellosis. Standard tube agglutination test (SAT), 2-mercaptoethanol (2-ME) agglutination, Coombs, immunocapture tests, and blood cultures were performed on these 211 blood samples. 190 sera belonging to healthy blood donors of endemic and non-endemic areas and 43 sera obtained from non-brucellosis patients were also subjected to SAT, 2-ME, Coombs, and immunocapture tests. A total of 15 blood cultures belonging to blood donors of endemic area and non-brucellosis cases were done.

RESULTS

SAT picked up only 21 (9.9%), Coombs established the diagnosis in 69 (32.7%), while the immunocapture test confirmed the diagnosis in 76 (36%; p < 0.001)) patients with brucellosis, including 48 culture-confirmed cases. Sensitivity and specificity of the immunocapture technique were 97.29% and 97.08% respectively. SAT could not exclude the diagnosis in 55 cases as they were confirmed in most cases by the Coombs test and in all by immunocapture.

CONCLUSIONS

Our results clearly show that immunocapture is superior to SAT in all stages of illness but is not significantly superior to Coombs. It also seems to be a useful tool in diagnosing a relapse. Immunocapture and Coombs tests were found to be more sensitive eliminating the ambiguity in the interpretation of the results for diagnosing brucellosis. The Coombs test is laborious, subjective in interpretation and demanding on skills. The immunocapture technique does not have the subjective reading errors, is simple to perform, and the results of the immunocapture technique seem to be reproducible. Thus we recommend the immunocapture technique especially for brucellosis-endemic countries. The Coombs, immunocapture, and 2-ME tests may also be considered useful tools in assessing treatment outcome.