Rapid enzyme-linked immunosorbent assay for the diagnosis of human brucellosis in surveillance and clinical settings in Egypt

OBJECTIVE: To optimize and standardize an enzyme-linked immunosorbent assay (ELISA) for rapid diagnosis of human brucellosis in clinical cases identified during a surveillance study for acute febrile illness (AFI).

METHODS: Serum samples from patients presenting with AFI at 13 fever hospitals across Egypt between 1999 and 2003 were kept frozen at NAMRU-3 and used in this study. The assay was evaluated in 5 subject groups: brucellosis cases confirmed by blood culture (group I, n=202) 87% positive by standard tube agglutination test (TA), brucellosis cases exclusively confirmed by TA (group II, n=218), blood cultures from AFI cases positive for bacterial species other than Brucella (group III, n=103), AFI cases with unexplained etiologies (group IV, n=654), and healthy volunteers (group V, n=50). All members of groups III-V were negative for brucellosis by TA.

RESULTS: Sensitivity and specificity of ELISA for total specific antibodies were >=96% versus 87% for TA as compared to microbial culture, the current gold standard method for Brucella identification. Assessment of Brucella antibody classes by ELISA in random subsets of the 5 groups showed significantly high (p>0.001) levels of anti Brucella IgG (>=81%) and IgM (>=90%) in groups I and II only.

CONCLUSION: The obtained sensitivity and specificity results indicate that our ELISA is more suitable for AFI surveillance and clinical settings than blood culture and TA. The developed assay is also cost-effective, easier to use, faster, and the coated plates can be stocked for at least 8 months, providing a potential for field use and automation.