Objective
To describe the epidemiology of SARS and to monitor the magnitude and the spread of this disease, in order to provide advice on prevention and control.

Case definitions (revised 1 April 2003)

The case definitions for global surveillance are subject to limitations because of the rapidly evolving nature of this illness. They are based on current understanding of the clinical features of SARS and the available epidemiological data, and may be revised as new information accumulates. Preliminary clinical description of Severe Acute Respiratory Syndrome summarizes what is currently known about the clinical features of SARS. Countries may need to adapt case definitions depending on their own disease situation. Retrospective surveillance is not expected.

Suspect case
1. A person presenting after 1 November 20021 with history of:
- high fever (>38 °C)
AND
- cough or breathing difficulty
AND one or more of the following exposures during the 10 days prior to onset of symptoms:
- close contact2 with a person who is a suspect or probable case of SARS;
- history of travel, to an affected area 3
- residing in an affected area 3

2. A person with an unexplained acute respiratory illness resulting in death after 1 November 2002, 1but on whom no autopsy has been performed
AND one or more of the following exposures during to 10 days prior to onset of symptoms:
- close contact,2 with a person who is a suspect or probable case of SARS;
- history of travel to an affected area 3
- residing in an affected area 3

Probable case
1. A suspect case with radiographic evidence of infiltrates consistent with pneumonia or respiratory distress syndrome (RDS) on chest X-ray (CXR).
2. A suspect case with autopsy findings consistent with the pathology of RDS without an identifiable cause.

Exclusion criteria
A case should be excluded if an alternative diagnosis can fully explain their illness.

Reclassification of cases
As SARS is currently a diagnosis of exclusion, the status of a reported case may change over time. A patient should always be managed as clinically appropriate, regardless of their case status.
- A case initially classified as suspect or probable, for whom an alternative diagnosis can fully explain the illness, should be discarded.
- A suspect case who, after investigation, fulfil the probable case definition should be reclassified as "probable".
- A suspect case with a normal CXR should be treated, as deemed appropriate, and monitored for 7 days. Those cases in whom recovery is inadequate should be re-evaluated by CXR.
- Those suspect cases in whom recovery is adequate but whose illness cannot be fully explained by an alternative diagnosis should remain as "suspect".
- A suspect case who dies, on whom no autopsy is conducted, should remain classified as "suspect". However, if this case is identified as being part of a chain transmission of SARS, the case should be reclassified as "probable".
- If an autopsy is conducted and no pathological evidence of RDS is found, the case should be "discarded".

1 The surveillance period begins on 1 November 2002 to capture cases of atypical pneumonia in China now recognized as SARS. International transmission of SARS was first reported in March 2003 for cases with onset in February 2003.

2 Close contact: having cared for, lived with, or had direct contact with respiratory secretions or body fluids of a suspect or probable case of SARS.

3 Affected area: an area in which local chain(s) of transmission of SARS is/are occurring as reported by the national public health authorities.