Comparison between LightCycler real-time polymerase chain reaction (PCR) assay with serum and PCR-enzyme-linked immunosorbent assay with whole blood samples for the diagnosis of human brucellosis

Background. To overcome some of the limitations of conventional microbiological techniques, polymerase chain reaction ( PCR) - based assays have been proposed as a useful tool for the diagnosis of human brucellosis. Methods. A single- blinded comparative study was undertaken that compared 2 different PCR assays: a SYBR Green I LightCycler- based Real- Time PCR assay ( LC- PCR; Roche Diagnostic) with serum samples and a PCR enzyme- linked immunosorbent assay ( ELISA) with whole blood samples. Both assays amplify a 223- bp sequence of a gene that codes for the synthesis of an immunogenetic membrane protein specific for Brucella genus ( BCSP31). We analyzed the diagnostic yield of these assays with 60 samples obtained from patients with active brucellosisand 37 samples obtained from a control group composed of patients with febrile syndromes of other defined etiologies, asymptomatic subjects with past brucellosis or exposure to Brucella infection who had persistently high titers of anti-Brucella antibodies, and healthy subjects. Results. The sensitivities of LC- PCR with serum samples, PCR- ELISA with whole blood samples, and blood cultures were 93.3%, 90%, and 65%, respectively. Three control samples ( 8.1%) had a positive PCR- ELISA result, and 2 of these samples ( 5.4%) also had positive LC- PCR results. The specificity and positivelikelihood ratios were 94.6% and 17.3, respectively, for LC- PCR and 91.9% and 11.1, respectively, for PCR- ELISA. Conclusions. The diagnostic yield of LC- PCR with serum samples was higher than that of PCR- ELISA with whole blood samples. The speed and technical simplicity of LC- PCR in serum samples make it a useful alternative to blood culturesfor patients with suspected brucellosis and negative or doubtful serological test results.