Emergencies preparedness, response

Recommendations for laboratories testing by PCR for presence of SARS coronavirus -RNA

29 April 2003

WHO encourages each country to designate a reference laboratory for investigation and/ or referral of specimens from possible SARS patients. National reference laboratories are welcome to send specimens and isolates to the members of the WHO multicentre collaborative network after appropriate contact and shipment arrangements have been made.

Laboratories performing SARS-specific PCR tests should adopt quality control procedures and /or identify a partner laboratory in their country or among the WHO collaborating research laboratories to cross-check their positive findings.

Laboratories performing SARS specific PCR tests should adopt strict criteria for confirmation of positive results, especially in low prevalence areas, where the positive predictive value might be lower:

- The PCR procedure should include appropriate controls in each run, which should yield the expected results. They should include:

  • 1 negative control for the extraction procedure and 1 water control for the PCR run
  • 1 positive control for extraction and PCR run
  • the patient sample spiked with a weak positive control to detect PCR inhibitory substances (inhibition control)

- If a positive PCR result has been obtained, it should be confirmed by:

  • repeating the PCR starting from the original sample OR
  • having the same sample tested in a second laboratory.

Amplifying a second genome region will increase test specificity.

A test kit with positive and negative control has been made available through the WHO collaborative multicentre research project on SARS diagnosis.