Evaluation of Brucella tube agglutination test in patients with brucellosis, patients with bacterial infections other than brucellosis and healthy subjects

Abstract

Results obtained by standard tube agglutination (STA) test which is the most widely used serological method for brucellosis, are often evaluated together with the clinical and microbiological findings, and the titers of ?1/160 are generally accepted as an indicator of acute infection. However, cross reactions with some other bacteria may lead to false positive results in this test. In this study, the performance of STA test in the diagnosis of brucellosis has been evaluated by using serum samples obtained from 40 culture positive brucellosis patients, 54 patients with bacterial infections other than brucellosis and 40 healthy blood donors. The distribution of infections and number of patients were as follows; urinary infection (n: 16), salmonellosis (n: 15), bacterial meningitis (n: 5), tuberculosis (n: 4), pneumoniae (n: 3), osteomyelitis (n: 3), infective endocarditis (n: 2), peritonitis (n: 2), diabetic foot infection (n: 2), acute cholecystitis (n: 1), and catheter infection (n: 1). STA were positive in all of the brucellosis patients between the titers of 1/160-1/1280 (mean: 1/640), whereas STA were found negative in all of the healthy subjects. Nevertheless two patients whose stool cultures yielded Salmonella spp., one patient whose urine culture yielded E.coli, one patient whose diabetic foot lesion culture yielded group A beta-hemolytic streptococci, exhibited STA positivity at the titers of 1/160. There was no history of brucellosis or presence of co-infections in the patients with non-brucellosis infections and blood donors. In conclusion, cross reactions due to the presence of other bacterial infections should be considered for the evaluation of Brucella STA test results, together with the endemicity of the country of interest and seropositivity rate of the population.