BacteriologyRelevance of autoantibody detection to the rapid diagnosis of brucellosis☆
Introduction
Brucellosis is a disease of protean manifestations, affecting various body organs, systems, and tissues (Young, 1991). The disease has diverse clinical features including fever, fatigue, sweating, arthralgia, loss of appetite, myalgia, lumbar pain, weight loss, headache, hepatomegaly, splenomegaly, and arthritis. It is generally included in the differential diagnosis of various diseases such as military tuberculosis, malaria, typhoid fever, hepatitis, systemic lupus erythematosus, rheumatoid arthritis, sarcoidosis, lymphoma, and other connective tissue diseases (Madkour, 2001). Diagnosis of brucellosis is still based mostly on the demonstration of specific antibodies by different serologic techniques. This is mainly because the greatest incidence of brucellosis is found in underdeveloped countries with poor technical resources, as well as the fact that it tends to occur in rural communities (Ruiz-Mesa et al., 2005). Because the symptoms of the brucellosis are not specific, confirmation can be reached by serologic tests, with significantly raised or rising titer, in the presence or absence of positive blood, body fluid, or tissue culture. Numerous serologic procedures have been tried in the diagnosis, but few have achieved lasting application (Altuglu et al., 2002, Mantecon et al., 2006). Until recently, the most widely used was the standard tube agglutination test (SAT). In many laboratories, this has now been superseded by the rose bengal plate test (Corbel & MacMillan, 1998). Determination of antinuclear antibodies (ANA), a heterogeneous group of autoantibodies against nuclear antigens, is useful for predicting some connective tissue diseases. ANA may occur in both physiologic and pathologic conditions. The presence of ANA cannot be used to discriminate between health and disease. In general, high titer (≥1/160) is a significant autoimmune disease indicator, but low or absent titer does not exclude diseases (Bradwell, 2002). Low-titer autoantibodies may be found in normal people, relatives of patients with autoimmune conditions, and a variety of diseases, such as chronic inflammation and cancer, which have no autoimmune basis and is frequently polyreactive, have low affinity, and are often of the immunoglobulin M class (Ulvestad et al., 2000). Autoantibodies also increase in prevalence with age, particularly in women, without necessarily being harmful (Bradwell, 2002).
The rose bengal test is often used for rapid diagnosis of human brucellosis in endemic areas. However, autoantibodies have never been investigated as a reason for false-positive or false-negative results. Therefore, the aim of this study was to show the effect of autoantibody detection on the rapid diagnosis of human brucellosis in an endemic area.
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Materials and methods
The samples included in this study were obtained for diagnostic purposes and routine testing from consecutive outpatients and inpatients of the Research Hospital, Kocaeli and Hifzissihha Institute, University of Kocaeli, Izmir, Turkey. Blood samples were taken for culture from patients who had clinical presentation compatible with brucellosis and were included in the study if Brucella was isolated. For ANA analysis, sera were submitted as part of the routine examination. Blood was collected by
Results
The study included 211 ANA-positive patients, including 2 patients with brucellosis, and 70 ANA-negative patients, including 30 patients with the brucellosis, totaling 281 individuals. A total of 281 rose bengal tests were performed. Of 281 individuals, 55 were found to be rose bengal positive. Of 55 positive results, 23 (41.8%) were false. In the study population with a 75.1% ANA-positive seroprevalence, the positive predictive value was 58.2%, whereas in the high-prevalence population (100%
Discussion
A large number of different tests have been used for the serologic diagnosis of brucellosis, thus demonstrating the lack of an ideal technique. Of the various rapid slide or plate agglutination tests for Brucella antibodies, the most effective is the rose bengal plate or card test. The test discriminates against agglutinins of low avidity and is not subject to prozones (Corbel & MacMillan, 1998). It compares favorably with the SAT in specificity and for detecting antibodies in human sera.
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This work was carried out at the Department of Clinical Microbiology, Faculty of Medicine, Kocaeli University, Kocaeli, Turkey, and the Clinical Microbiology Laboratory, Hifzissihha Institute, Izmir, Turkey.