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Update: Severe Acute Respiratory Syndrome --- Worldwide and United States, 2003

This report updates reported cases of severe acute respiratory syndrome (SARS) worldwide and in the United States, describes a change in the recommended timing of collection of a convalescent-phase serum specimen to test for antibody to SARS-associated coronavirus (SARS-CoV), and introduces a new case exclusion criterion based on negative SARS-CoV serology (1). In addition, this report also summarizes changes in travel alerts for Beijing and mainland China, Hong Kong, Toronto, and Taiwan.

During November 1, 2002--July 11, 2003, a total of 8,427 probable SARS cases were reported to the World Health Organization (WHO) from 29 countries; 813 deaths (case fatality rate: 9.6%) have been reported, with no SARS-related deaths in the United States (2). On July 5, WHO announced that all known person-to-person transmission of SARS-CoV had ceased (3).

CDC has revised the laboratory criteria in the SARS case definition to require that convalescent serum be collected >28 days after symptom onset, instead of >21 days after symptom onset. This change reflects data that some persons with SARS-CoV infection might not mount a detectable antibody response until >28 days after illness onset (4). Because most persons without immune-compromising conditions are thought to mount an immune response within 28 days, test results from serum collected previously 22--28 days after symptom onset will be considered definitive. However, state and local health officials can choose to collect a later specimen on a case-by-case basis if they consider it to be indicated clinically.

On June 26, the Council of State and Territorial Epidemiologists changed the U.S. SARS case definition to allow exclusion of cases with a negative convalescent serum specimen. This change reflects data indicating that >95% of patients with SARS mount a detectable convalescent antibody response (4,5). The U.S. case numbers in this report reflect this exclusion criterion.

As of July 15, a total of 418 SARS cases were reported in the United States, with 344 (82%) classified as suspect SARS and 74 (18%) classified as probable SARS (i.e., more severe illnesses characterized by the presence of pneumonia or acute respiratory distress syndrome). A total of 169 reported suspect cases and 38 reported probable cases were excluded because the convalescent serum specimen was negative for SARS-CoV antibodies (Table). None of the reported suspect cases and eight reported probable SARS cases had a convalescent serum specimen that was positive for SARS-CoV antibodies; these eight laboratory-confirmed SARS cases have been reported previously (6--8). Convalescent serum specimens have not been obtained for the other 28 reported probable cases and 175 reported suspect cases; therefore, it is not known whether these persons had SARS.

Serologic testing results suggest that a small proportion of persons who had illness consistent with the clinical and epidemiologic criteria for a U.S. case of suspect or probable SARS actually had SARS. The case definition captures an array of respiratory illnesses that cannot be easily distinguished from SARS until laboratory testing results for SARS and other agents are performed. However, this sensitive case definition allowed for rapid investigation of persons who might have had SARS and for public health intervention to prevent person-to-person transmission.

CDC lifted the travel alerts for Beijing and mainland China, Hong Kong, Toronto, and Taiwan during July 1--15, 2003 (9); CDC's criteria for lifting an alert for SARS include the absence of new cases for three incubation periods (i.e., 30 days) after the date of onset of symptoms for the last reported case (http://www.cdc.gov/ncidod/sars/travel_alertadvisory.htm). For traveler's illness to meet the case definition for SARS, the travel should have occurred on or before the last date the travel alert was in place. In addition, the last date for illness onset is 10 days (i.e., one incubation period) after removal of a CDC travel alert (1). With removal of all SARS travel alerts and completion of an incubation period, U.S. travelers with respiratory illness will no longer meet the case definition for SARS; reports of suspect or probable cases are expected to end by the end of July 2003.

References

  1. CDC. Updated interim U.S. case definition for severe acute respiratory syndrome (SARS). Available at http://www.cdc.gov/ncidod/sars/casedefinition.htm.
  2. World Health Organization. Cumulative number of reported cases of severe acute respiratory syndrome (SARS). Available at http://www.who.int/csr/sars/country/2003_07_11.en.
  3. World Health Organization. SARS outbreak contained worldwide. Available at http://www.who.int/mediacentre/releases/2003/pr56/en.
  4. Peiris JSM, Chu CM, Cheng VCC, et al. Clinical progression and viral load in a community outbreak of coronavirus-associated SARS pneumonia: a prospective study. Lancet 2003;361:1767--72.
  5. Rainer TH, Cameron PA, DeVilliers S, et al. Evaluation of WHO criteria for identifying patients with severe acute respiratory syndrome out of hospital: prospective observational study. BMJ 2003;326:1354--8.
  6. CDC. Update: severe acute respiratory syndrome---United States. MMWR 2003;52:550.
  7. CDC. Update: severe acute respiratory syndrome---United States. MMWR 2003;52:570.
  8. CDC. Update: severe acute respiratory syndrome---United States. MMWR 2003;52:616.
  9. CDC. SARS information for travelers. Available at http://www.cdc.gov/ncidod/sars/travel.htm.
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