Diagnostic Tests

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Diagnostic Tests

• Wolfgang Preiser
• Christian Drosten
• Prepared by
• ABM Alauddin Chowdhury

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Early Diagnostic Tests

• Early diagnosis needed use of highly sensitive
  tests
• Available tests are unable to detect small
  amounts of SARS coronavirus.

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Pictures of SARS

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Laboratory Tests

• Efforts of WHO-led international multi-center
  collaborative network
• Standardized reagent for virus and antibody
  detection

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Laboratory Tests (Continued)

• Revised case definition from may 1, 2003,includes
  laboratory results for the first time
• Positive laboratory test results for other known
  agents are able to cause atypical pneumonia

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Chest x-ray showing Pneumonia
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Molecular Tests PCR

• SARS- CoV-specific RNA can be detected in various
  clinical specimens by PCR
• Valid positive PCR result
• Negative PCR results
• Efforts are underway to improve the sensitivity
  of PCR assays

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Virus Isolation

• Cell culture is a very demanding test.
• Performed under biosafety safety level 3
  conditions
• Positive cell culture indicates presence of live
  SARS-CoV in sample tested.
• Negative cell culture results do not exclude SARS.

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Antibody Detection

• Enzyme-linked Immunosorbent Assay
• Immunofluorescence Assay
• Neutralization Test

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Limitations

• Caution urged when using diagnostic tests
• False negative test results may give a false
  sense of security.
• Allow persons carrying the SARS virus

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WHO Recommendations

• Patient samples suitable for viral culture, PCR,
  antigen detection, immunostaining
• Designate a reference laboratory for investigation

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Table1. Diagnostic Tests
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Figure1. Immunofluorescence assay
SourceInstitute for Medical Virology, Director.
W.Doerr

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Figure 2. Immunofluorescence assay
SourceInstitute for Medical Virology, Director.
W.Doerr

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Figure 3. Amplification plot of TaqMan
Picture source Institute for Medical
Virology,Director W.Doerr.
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Biosafety considerations

• WHO has issued biosafety
• guidelines
• BSL-2 work practices
• BSL-3 work practices

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Containment Facilities and Biosafety Practices

• Specimens to be transported (UN 3373 or UN 2814)
  must be packaged in triple packaging consisting
  of three packaging layers

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Availability of diagnostic tests help to address

• Period of virus shedding during convalescence
• Presence of virus in different body fluids and
  excreta
• Presence of virus shedding during the incubation
  period

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Degree of standardization and quality assurance

• Test results must be used with utmost caution in
  clinical situation.
• All laboratory test methods for SARS-CoV require
  careful evaluation before valid results can be
  used.
• Use of WHO recommended Tests