New Criteria Halves U.S. SARS Cases
Antibody Screening Tests Rule Out Non-SARS Illness
July 18, 2003 -- The number of SARS (severe acute respiratory syndrome) cases reported in the U.S. has dropped by half, thanks to a new case definition that excludes those who test negatively for the SARS virus.
The new totals include 175 suspect cases and 36 probable cases currently being monitored in the U.S., down from 344 suspect and 74 probable cases reported on July 15.
The CDC adopted the new case definition based on research that shows 95% of SARS patients have a detectible immune system response to the SARS virus. The immune system develops antibodies to the SARS virus that show up in blood tests that screen for these antibodies at least 21-28 days after the start of illness.
Officials say excluding those patients with SARS-like respiratory symptoms and travel history that test negatively for SARS antibodies will allow for more accurate accounting of the SARS epidemic in the U.S.
In addition, the CDC changed its recommendation for the timing of SARS antibody tests from 21 to 28 days after the onset of illness. Recent information has shown that some people infected with the SARS virus may not have a detectible antibody response until 28 days after the start of illness.
The World Health Organization (WHO) announced earlier this month that the current SARS outbreak has been contained, and the CDC expects that reports of both suspect and probable SARS cases in the U.S. to end by July 31.