Comparison%20of%20the%20Diagnostic%20Value%20of%20the%20Standard%20Tube%20Agglutination%20Test%20and%20the%20ELISA%20IgG%20and%20IgM%20in%20Patients%20with%20Brucellosis

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Ahlan Wa Sahlan, Mahe Ramadan Assalamualaikum
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Welcome to Journal Club Department of
Microbiology, MMC
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Comparison of the diagnostic value of STA test
and ELISA IgG and IgM in patients with
BrucellosisMustafa Ertek, Halil Yzgi, Zulal
Ozkart et al. Turk J Med Sci 2006 36(3)
159-163
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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

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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

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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

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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

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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

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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)

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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
  120 up to 1160 or gt
• Samples with an antibody titer of 1160
  considered positive

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Results

• Study Group (n32)
• SAT Positive 30/32
• Brucella IgG ELISA positive 26/32
• Brucella IgM ELISA positive 32/32
• Both IgG and IgM positive 24/32
• Control (n20)
• All were negative (titerlt1/80) in SAT, 1 was
  positive in ELISA IgG and 3 were positive in
  ELISA IgM

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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

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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

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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

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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

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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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Thanks to all