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Introduction

Comparison of the diagnostic value of STA test and ELISA IgG and IgM in patients with Brucellosis Mustafa Ertek, Halil Yzgi, Zulal Ozkart et al . Turk J Med Sci 2006 ; 36(3) : 159-163. Introduction. Brucellosis is a zoonotic disease

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Introduction

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  1. Comparison of the diagnostic value of STA test and ELISA IgG and IgM in patients with BrucellosisMustafaErtek, Halil Yzgi, Zulal Ozkart et al. Turk J Med Sci 2006 ; 36(3) : 159-163

  2. Introduction • Brucellosis is a zoonotic disease • Affect men and close animals, e.g- the cattle, camel and pig • Brucella enter hosts • orally via contaminated dairy products and animal feed • Through the respiratory tract via aerosols • through skin via contact with infected animals on farms or in slaughterhouses

  3. Introduction • Since the symptoms of brucellosis are non-specific, diagnosis of it is difficult clinically • Diagnosis must be supported and confirmed by isolation of the agent from blood culture (gold standard) or detection of antibodies against bacterial antigens • The isolation rate from blood cultures ranges from 47.1% to 94.1% • Rising titers of specific antibodies- highly diagnostic

  4. Introduction • A variety of serologic tests have been applied of which the standard agglutination test (SAT) is the most widely used • More recently, the Brucella ELISA is introduced into clinical laboratories • The aim of this study- to compare the diagnostic value of SAT with that of Brucella ELISA tests

  5. Materials and Methods • Design: Case- Control • Place: Department of Clinical Bacteriology and infectious diseases, Ataturk University Medical school, Turkey • Period: 2005 • Subjects: 32 patients of brucellosis who had positive blood and/or bone-marrow cultures and 20 healthy individuals as controls • Both patients and controls were from the same epidemiological area

  6. Methods • Laboratory procedure • Blood culture of 2 samples (10 ml each) • Bone marrow culture of one sample as sternal aspirate (1 ml) • Primary culture by BACTEC9240 with incubation time of 21 days • Subculture in Blood agar and chocolate agar • No grpwth on 21 days Gram staining and a blind subculture were performed

  7. Materials and Methods • Identification and species detection • The isolates of Gram-negative cocco-bacilli were identified by motility, oxidase, catalase and urease activity, glucose fermentation and production of H2S). • Species were identified by slide agglutination using type-specific antisera (Murex Diagnostics, Dartford, UK)

  8. Materials and Methods • Fifty-two sera samples from both groups were tested for Brucella specific IgG and IgM antibodies by ELISA using a commercial kit (Novum, Germany) • The test was performed and evaluated according to the kit procedure • The same samples were also tested by SAT using B.abortus antigen with starting dilutions from 1:20 up to 1:160 or > • Samples with an antibody titer of ≥1:160 considered positive

  9. Results • Study Group (n=32) • SAT Positive: 30/32 • Brucella IgG ELISA positive: 26/32 • Brucella IgM ELISA positive: 32/32 • Both IgG and IgM positive: 24/32 Control (n=20) • All were negative (titer<1/80) in SAT, 1 was positive in ELISA IgG and 3 were positive in ELISA IgM

  10. Results • Sensitivity, specificity, PPV and NPV of SAT was 93.7%, 100%, 100% and 90.9% • Sensitivity, specificity, PPV and NPV of ELISA IgG was 81.3%, 95%, 96.3% and 76% • Sensitivity, specificity, PPV and NPV of ELISA IgM was 93.8%,85%,90.9% and 89.5 • Sensitivity, specificity, PPV and NPV of ELISA IgM and IgG was75%, 94.4%,96% and 68%

  11. Discussion • Low titre of antibodies can give SAT negative result in early infection, rising titre should be done • Prozone phenomenon (antibody excess) may give negative agglutination, need test at higher dilution • Blocking antibodies may give negative agglutination • Cross reaction to Salmonella, Yersinia, Vibrio, Fransicella, Esch.coli may give false positive results

  12. Discussion • SAT negative cases should be tested by ELISA for specific IgG and/or IgM due to its superior sensitivity • IgG is better sensitive and specific in sub-acute and chronic cases, IgM is less. Findings of the present study correlated with this view • Many other studies were compared • False positive ELISA for IgM may appear due to non-specific binding of B.abortus LPS to IgM

  13. Conclusion • The overall data in the present study showed that the sensitivity of SAT and ELISA IgM tests were nearly equal • but the sensitivity of ELISA IgG was lower than that of the other two • On the other hand, the specificity of SAT was higher than that of both ELISA IgG and IgM • According to the results of the study, SAT may be preferred to ELISA in acute brucellosis because it is cheap and easily applicable

  14. Key message Brucellosis is better diagnosed by combination of SAT and ELISA (IgG & IgM) when blood culture produce negative result or facilities are not available

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