Diagnostic Sensitivity of Blood Culture, Serology, and Molecular Methods in the Detection of Brucella Infection

Clinical manifestations of brucellosis in humans are variable and nonspecific, therefore laboratory confirmation for appropriate treatment of the patient is essential. Brucella infection can be diagnosed by culture, serological tests, and nucleic acid amplification−based methods. The present study was conducted to investigate the molecular and seroepidemiological aspects of clinically suspected brucellosis patients in northeastern Iran. A total of 800 blood and serum samples were obtained from individuals presenting to medical centers in eastern and northeastern cities of Iran with clinical manifestations suggestive of brucellosis, including fever and chills, night sweats, recurrent and prolonged fever, weight loss, anorexia, and joint inflammation. The patients comprised of 66% men and 34% women, ranging in age from 12 to 86 years, with the most common age group being 25–45 years. Fever was the most frequently reported symptom (38%), and 51.5% of the patients had a documented history of contact with livestock. Cultures prepared from the collected samples identified 44 positive cases using standard biochemical methods. Then, the samples were evaluated using the Wright test, 2-mercaptoethanol, ELISA, PCR for the omp31 gene, and real-time PCR for the bcsp31 gene. All isolated strains were identified as Brucella melitensis. In this study, the real-time PCR (targeting bcsp31) showed the highest sensitivity (77.27%), followed by the Wright test (75%) and PCR (omp31 gene) (72.72%). Culture with 58.1% had the lowest diagnostic sensitivity. Out of the total of 33 positive samples reported with the Wright test, 24 samples (72.72%) showed positive results in the 2 ME test. Using the ELISA method, IgG was detected in 22 samples (47.82%), and IgM was detected in 14 samples (30.43%) out of 44 investigated samples. The results of the present study highlight the necessity of using multiple diagnostic techniques to diagnose human brucellosis in addition to the clinical symptoms of suspected patients. In addition, the bcsp31 real-time PCR assay showed superior sensitivity compared to other methods. Given that serological methods still serve as the primary tools for estimating brucellosis prevalence, incorporating real-time PCR assays may help overcome the limitations of conventional diagnostics.