Use of Laboratory Methods for SARS Diagnosis

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Recommendations on interpretation of laboratory results: Positive SARS diagnostic test findings

  1. Confirmed positive PCR for SARS virus
    • at least 2 different clinical specimens (e.g., nasopharyngeal and stool) OR
    • the same clinical specimen collected on 2 or more days during the course of the illness (e.g., 2 or more nasopharyngeal aspirates) OR
    • 2 different assays or repeat PCR using the original clinical sample on each occasion of testing
  2. Seroconversion by ELISA or IFA
    • negative antibody test on acute serum followed by positive antibody test on convalescent serum OR
    • four-fold or greater rise in antibody titre between acute and convalescent phase sera tested in parallel
  3. Virus isolation
    • Isolation in cell culture of SARS-CoV from any specimen; plus PCR confirmation using a validated method.

(Reference: World Heath Organization)

Confirmation of positive PCR

Amplifying a second genome region could further increase test specificity

Recommendations for laboratories testing for SARS

Reference laboratories should be identified at national level.

Antibody testing

ELISA and IFA tests are being developed by research laboratories. Because SARS a new disease in humans, SARS-CoV antibodies are not found in populations that have not been exposed to the virus. An antibody rise between acute and convalescent phase sera tested in parallel is very specific.