Comparison of the Rose Bengal and ELISA Tests with the Standard Tube Agglutination Method in the Diagnosis of Brucellosis

Abstract

Brucellosis, an infectious bacterial zoonotic disease caused by bacteria of the Brucella genus, can cause high morbidity and is rarely associated with mortality. In order to guide clinicians in the rapid and accurate diagnosis of brucellosis, it is of great importance to use easy-to-apply and highly sensitive and specific screening tests in microbiology laboratories. This study included 1,709 patients that presented to our hospital with various complaints (mainly joint complaints, fever, and fatigue) compatible with brucellosis and underwent the Rose Bengal test (RBT), Brucella ELISA IgM and IgG tests, standard tube agglutination (STA) test, and Coombs agglutination tests between January 2020 and December 2020. All the laboratory tests were performed in standard laboratory conditions in accordance with the manufacturer's recommendations. The department to which the patients presented, their test results, regions of birth, age and gender data were reviewed retrospectively. The first three clinics to which the patients presented were rheumatology (27.8%), infectious diseases (18.4%), and internal medicine (11.1%). We followed two different paths when comparing the test results. In the first approach, we considered patients with at least one positive test result as seropositive and analyzed the results of the remaining tests in the same patients. In the second approach, we compared the results of the RBT and ELISA tests with the reference tests of STA and Coombs agglutination.Of a total of 3,365 tests evaluated for 1,709 patients, 7.43% (127/1,709) were seropositive according to at least one method. According to this initial approach, the sensitivities of all the serological tests ranged from 20.4% to 49.3%, and their specificities ranged from 93.8% to 100%. In the second approach, based on confirmatory tests, the sensitivities of the screening tests were 100%, 100% and 84.6% for RBT, ELISA IgG and ELISA IgM, respectively, while their specificities were 90.6%, 81% and 63.8%, respectively. These findings indicate that serological methods can be significantly misleading in the diagnosis of brucellosis if the test results are not combined. Although the number of seropositive cases was low, we obtained results consistent with the regional prevalence data when we distributed the patients according to their place of birth.In conclusion, since there is no gold standard test for the serological diagnosis of brucellosis, the test results should be combined based on the advantages and disadvantages of each test. It is important to evaluate the laboratory diagnosis together with the patient symptoms and complaints consistent with the disease and to consider epidemiological details in this process.