Clinical utility of a quantitative Rose Bengal slide agglutination test in the diagnosis of human brucellosis in an endemic region.

BACKGROUND: Brucellosis currently ranks as the most important zoonotic disease in the world. Brucellosis is difficult to diagnose because patients often have nonspecific clinical symptoms that can be attributed to a number of disease agents prevalent in the area. Thus, this has necessitated the dependency of clinicians on microbiological confirmation, very often by sero diagnostic methods. Early and accurate detection of brucellosis is important if specific antibiotic treatment is to be effective for the patients. The use of RBST as a qualitative means of diagnosis is quiet common. However, to date, there are only a handful of reports of the application of RBST as a quantitative diagnostic method in medical literature. The potential usefulness of quantitative Rose Bengal slide agglutination test (RBST) for suspected brucellosis was evaluated as a simple, inexpensive diagnostic tool to be used in clinical practice in an endemic region. METHODS: 200 consecutive patients who reported to Belgaum Institute of Medical Sciences (BIMS) Hospital, Belgaum, Karnataka (India) between June 2009 and December 2011 were studied. Standard RBST, quantitative RBST, standard tube agglutination test (SAT), 2-mercaptoethanol test (2-ME), and blood cultures were carried out on all patients. The case was confirmed as positive for brucellosis if any one of the tests was positive and the data was compared to the quantitative RBST considering blood culture result as gold standard. RESULTS: B. melitensis was cultured in only 28% of the patients in this study. In patients with negative blood cultures, serology was used for diagnosis. The sensitivities were 88.9% (standard RBST), 92.6% (SAT), and 57.4% (2ME). The specificities were found to be 87.7% (standard RBST), 86.2% (SAT), and 95.7% (2ME). RBST titers > or = 1:8 were detected in a majority of patients (50, 74%) with bacteriologically proven brucellosis thereby guiding clinician for prompt therapy. Prozone reaction with RBST observed in 4 patients was an interesting finding and these four true cases would have been underdiagnosed and denied therapy on the basis of qualitative/standard RBST alone. The possibility of prozone in patient's serum with high RBST antibody titers can be avoided by testing several dilutions. CONCLUSIONS: This technique has an immense value particularly for use in resource poor settings seen in rural areas. It can deliver definitive diagnosis in < 10 minutes to the clinician, which may in turn result in the early initiation of specific treatment and could be applied thus as a bedside methodology. It is not technically demanding and easy to interpret, does not involve heavy capital outlay, or trained personnel and, thus, is potentially useful in resource poor laboratories, particularly in developing regions. In addition, quantitative RBST demonstrates sensitivity and specificity equivalent to that achievable by performing SAT. It can readily be extended to screen a vast number of blood samples particularly in areas where brucellosis is hyperendemic. Quantitative RBST and 2ME have been noted to be of great value in therapeutic monitoring. Our data suggest that RBST titers in a range of 1:8 and 1:16 can undoubtedly be considered diagnostic of brucellosis in conjunction with compatible clinical and epidemiological evidence for the patients residing in areas endemic for the disease. Quantitative RBST is, therefore, recommended for routine use in clinical microbiology laboratories as an accurate and speedy diagnostic assay.

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.