Evaluation of PCR, culture and serology for the diagnosis of acute human brucellosis

Background: The diagnosis of brucellosis is frequently difficult to establi sh. This is not only because clinically, the disease can mimic any infectio us and noninfectious disease, but also because the established diagnostic m ethods are not always successful. In this study, we have tried to evaluate PCR techniques in the diagnosis of brucellosis in comparison to conventiona l techniques. Patients and Methods: Fifty peripheral blood samples from the following gro ups were collected: patients with brucellosis (17); patients with febrile i llnesses due to factors other than brucella etiology (19); symptomatic occu pationally exposed persons (9); and healthy volunteers (5). The last three groups were considered controls. Among the 17 Brucella samples, only 14 wer e obtained before treatment was begun. The samples were tested by serology, using the standard tube agglutination method (STA), blood culture using Ba ctec machines, and PCR using primer pair to amplify a 223-bp region within a gene coding for a 31-kD Brucella antigen. Diagnosis of brucellosis was ba sed on compatible clinical picture in addition to positive blood culture an d/or positive serology. Results: Of the 17 blood samples from patients with brucellosis, eight were culture positive for Brucella species, and all showed high titer antibruce lla antibodies. Only 14 of them were positive by PCR, and these were the sa mples submitted before initiation of therapy, representing 100% sensitivity . Among the 33 controls, blood culture was negative for Brucella in all of them, while one sample showed high-titer antibrucella antibodies. The latte r was from the febrile illnesses group. PCR-based assay was able to detect four bands in the controls, all of which were from the occupationally expos ed asymptomatic group. Conclusion: in view of the several advantages of PCR over the conventional methods for the diagnosis of brucellosis, such as speed, safety, high sensi tivity and specificity, the technique might be considered for laboratory di agnosis of brucellosis. However, for the evaluation of asymptomatic highly exposed persons, PCR might be considered complementary to the traditional m ethods and followed up by serology and/or culture.