Update to SARS Case Definition Reduces US Cases by Half

The Centers for Disease Control and Prevention (CDC) has dropped the number of SARS cases in the United States by half (49.5%) to a total of 211. The new tally, reported in today’s Morbidity and Mortality Weekly Report (MMWR), includes 175 suspect cases and 36 probable cases, down from 344 suspect and 74 probable cases reported on July 15. The change results from excluding cases in which blood specimens that were collected more than 21 days after the onset of illness test negative for SARS-associated coronavirus (SARS-CoV). Exclusion of these cases with negative convalescent serum provides a more accurate accounting of the epidemic in the US.

The Council of State and Territorial Epidemiologists, an association of public health professionals in US states and territories, recommended the change in the US SARS case definition to allow for exclusion of cases with negative convalescent serum specimens. This recommendation is based on scientific data which indicate that 95% of SARS patients mount a detectable convalescent antibody response.

Additionally, today’s MMWR recommends changing the timing for collecting convalescent-phase serum specimens to test for antibody to SARS-CoV from 21 or more days to 28 or more days after the onset of illness. This recommendation comes following analysis of recent data which indicate that some persons with SARS-CoV infection may not mount a detectable antibody response until 28 days after the onset of illness. However, testing results from serum previously collected between 22 and 28 days are acceptable and will not require collection of an additional sample.

CDC lifted all travel alerts related to SARS between July 1 and 15. With removal of all SARS travel alerts and completion of an incubation period (10 days), U.S. travelers with respiratory illness will no longer meet the current case definition for SARS. Reports of suspect or probable cases, therefore, are expected to end by July 31, 2003.

For more information about the SARS case definitions, see the CDC web site at http://www.cdc.gov.

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