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ATLANTA -- The Centers for Disease Control and Prevention (CDC) has added laboratory criteria for evidence of infection with the SARS-associated coronavirus (SARS-CoV) to its interim surveillance case definition. CDC Director Dr. Julie L. Gerberding announced a new category, laboratory-confirmed, at a Senate committee hearing on SARS on Tuesday.
A total of 274 cases of SARS have been reported in the United States; 222 are suspect cases and 52 are probable. Of the 52 probable SARS cases reported as of April 29, 2003, 6 are laboratory-confirmed using the new laboratory criteria. Twelve cases are considered probable, but are not laboratory-confirmed, either because the laboratory tests are not sensitive enough to pick up the SARS virus or because the illness was not caused by SARS virus. Laboratory results are undetermined for the remaining 34 probable cases; for some, testing is in progress and for others suitable specimens are not available for testing.
Using the new laboratory criteria, a SARS case is laboratory-confirmed if one of the following is met:
Â· Detection of antibody to SARS-CoV by indirect fluorescent antibody (IFA) or enzyme-linked immunosorbent assay (ELISA)
Â· Isolation of SARS-CoV in tissue culture
Â· Detection of SARS-CoV RNA by reverse transcriptase-polymerase chain reaction (RT-PCR), which must be confirmed by a second PCR test
Negative laboratory results for PCR, viral culture, or antibody tests obtained within 21 days of illness do not rule out coronavirus infection. In these cases, an antibody test of a specimen obtained more than 21 days after illness begins is needed to determine infection.
Most U.S. cases of SARS continue to be associated with travel; a small number of cases have resulted from secondary spread to household members or healthcare workers. CDC will continue to update the SARS case definition as new data become available, or if there are changes in the spread of SARS illness in the United States.