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Defining surveillance

Print edition : May 23, 2003 T+T-

The following are the World Health Organisation's (WHO) case definitions for the surveillance of SARS, as on March 16, 2003:

Suspect case*

A person presenting after February 1, 2003 with a history of high fever ({gt}38{+o}C) (100.4{+o}F) and one or more respiratory symptoms, including cough, shortness of breath, difficulty breathing and one or more of the following:

Close contact*, within 10 days of onset of symptoms, with a person who has been diagnosed with SARS;

History of travel, within 10 days of onset of symptoms, to an area in which there are reported foci of transmission of SARS.

Probable case

A `suspect' case with chest x-ray findings of pneumonia or Respiratory Distress Syndrome (RDS), or a person with an unexplained respiratory illness resulting in death, with an autopsy examination demonstrating the pathology of RDS without an identifiable cause.

(In addition to fever and respiratory symptoms, SARS may be associated with other symptoms, including headache, muscular stiffness, loss of appetite, malaise, confusion, rash and diarrhoea.)

On May 1, the above specifications were revised to incorporate data from surveillance based on laboratory tests that are beginning to be adopted widely in many countries, including India. The key changes that were made are:

1. The beginning of the surveillance period was pushed back to November 1, 2002, in the light of the confirmation that the outbreak in Guangdong, China, in November was indeed that of SARS.

2. A `suspect' case in whom recovery is adequate but whose illness cannot be explained fully by an alternative diagnosis should remain as `suspect'.

3. A `suspect' case of SARS that has proved positive for SARS-coronavirus (SARS-CoV) in one or more laboratory assays should be reported as a `probable' case.

4. `Suspect' cases with positive laboratory results will be reclassified as `probable' cases for notification purposes only if the testing laboratories use appropriate quality control procedures.

5. No distinction will be made between `probable' cases with or without a positive laboratory result and `suspect' cases with a positive result for the purposes of global surveillance.

6. Cases that meet the surveillance case definition for SARS should not be discarded on the basis of negative laboratory tests at this time.

* Close contact means having cared for, having lived with, or having had direct contact with respiratory secretions and body fluids of a person with SARS.