[The value of culture and serological methods in the diagnosis of human brucellosis]

Abstract

Human brucellosis is a potentially life-threatening multisystem disease. During the first week of infection, IgM antibodies against lipopolysaccharide antigens appear in the serum, followed by IgG antibodies as early as the second week. Both antibody isotypes peak during the fourth week, and the use of antibiotics was associated with a decline of both IgM and IgG class antibodies. The diagnosis of brucellosis is based on a detailed history obtained from the patients and the isolation of Brucella spp. from blood cultures are accepted as the standard method. The definitive diagnosis of brucellosis requires isolation of the bacterium from blood, bone marrow or tissue samples. Although the sensitivity of blood culture method varies depending on the individual laboratory practices, quantity of bacteria in blood and the methods used, it changes between 15-70 percent. Bone marrow culture is considered as the gold standard for the diagnosis of brucellosis, since the relatively high concentration of Brucella in reticuloendothelial system enables the detection of the organism. The standard tube agglutination test (SAT) is the most widely used serologic test for the confirmation of human brucellosis. The detection of seroconversion or high antibody titers (> or = 1/160) are considered diagnostic together with a compatible clinical presentation. The lack of seropositivity in patients with strongly suspected clinical picture may be attributed to the performance of tests early in the course of infection, the presence of blocking antibodies (non-agglutinating, incomplete) or the so-called "prezone" phenomenon. Enzyme immunoassays (ELISA) which measure specific IgM, IgG and IgA antibodies, allow for a better interpretation of the clinical situation and overcome the false negativities/positivities which may arise in SAT. In this review article, the use and the values of culture methods and serological tests (Rose-Bengal test, SAT, Coombs' test, mercaptan-based tests, dipstick assay, flow assay, ELISA and brucellacapt) in the diagnosis of brucellosis have been discussed.