The interim US surveillance case definition for severe acute respiratory syndrome (SARS) was revised in July to allow for exclusion of cases with negative convalescent-phase serology. Using the revised criteria, the US Centers for Disease Control and Prevention (CDC) excluded nearly half of the 418 reported cases of SARS in the USA to date.
According to CDC epidemiologist Umesh Parashar (Division of Viral and Rickettsial Diseases, National Center for Infectious Disease, Atlanta, GA, USA), “In the end, we only have eight cases of SARS confirmed by serology in the USA. None of the suspect SARS cases to date were positive”.
“WHO has repeatedly asked countries to reclassify their SARS cases and to discard them only if they are fully explained by another cause”, WHO spokesperson Maria Cheng told TLID. “Reclassification also refers to upgrading suspect to probable cases on the basis of positive laboratory tests.”
On June 11, the Council of State and Territorial Epidemiologists (CSTE), a US professional public-health organisation, issued a policy statement calling on the CDC to take specific steps that would improve surveillance for SARS in the USA (http://www.cste.org/PS/2003pdfs/2003finalpdf/03id12%20SARS2003_final.pdf). CSTE recommends in the statement that the US surveillance case definition be revised and split into two cases definitions, one for SARS reports under investigation and one for reports of SARS-coronavirus disease.
“The more sensitive SARS reports under investigation reflect a group where you want to detect these cases and identify them so you can institute infection control and other measures to prevent transmission, but you don't necessarily want to report them as cases of SARS”, said Parashar, who coauthored the position statement with James Hadler (Infectious Diseases Division, Connecticut Department of Public Health, Hartford, CT, USA).
In addition to a revised case definition, CSTE requests in the statement that the CDC include cases of SARS-coronavirus disease as a notifiable disease in the National Public Health Surveillance System.
Testing for SARS
© 2003 CDC/Anthony Sanchez
The CSTE position statement and case definition has not been fully adopted by the CDC. “A final version is expected to be published soon in an upcoming Morbidity and Mortality Weekly Report”, Parashar told TLID.
Coinciding with the revised exclusion criteria for SARS, CDC adjusted the recommended timing of collection of the convalescent-phase serum sample, because in some cases antibody response to SARS-coronavirus infection may not be detectable until 28 days after the onset of illness.
CDC has made reagents for SARS-coronavirus antibody testing available to state public-health laboratories.