But in a confusing development, at least one of the researchers asked that the letter reporting the case be withdrawn from publication in the New England Journal of Medicine. Editors of the medical journal said they were trying to find out why.
The letter was available to journalists before its withdrawal, and describes the case of a 24-year-old man who died from pneumonia and respiratory distress in November 2003.
"Because the clinical manifestations were consistent with those of the severe acute respiratory syndrome (SARS) and occurred when sporadic cases of SARS were described in southern China, serum and lung tissue from the patient, as well as fluid aspirated from his chest, were examined for SARS coronavirus," the researchers wrote. "All tests were negative for SARS."
The World Health Organisation said it was asking China's Ministry of Health for clarification.
"This has been signed by eight scientists from very prestigious institutions. It certainly adds weight to the information," said Roy Wadia, WHO spokesman in China.
SARS first broke out in China's southern Guangdong province in 2002 and spread as far afield as Canada before it was brought under control in 2003. It killed close to 800 people out of the 8,000 known to have been infected.
Ironically, experts at the time assumed the then-mysterious illness making people sick in China was H5N1 avian influenza, which broke out in Hong Kong in 1997 and then disappeared.