Researchers find two distinct SARS strains

Finding could foretell resurgence

Tsui SKW, Chim SSC, Dennis Lo YM. Corre-spondence: Coronavirus genomic-sequence variations and the epidemiology of the severe acute respiratory syndrome. N Engl J Med 2003; 349:187-188.

In a finding that may foretell resurgence of severe acute respiratory syndrome (SARS), researchers in China have found that there may be two distinct strains behind the global SARS outbreak.

"These results emphasize the need for vigilance in order to prevent the resurgence of this disease," the authors warned.

Their teaching hospital was the site of a major outbreak of SARS. The researchers sequenced viral isolates cultured from clinical specimens from seven patients with SARS in the outbreak. They obtained the complete genomic sequence of the virus cultured from the mother of the index patient in the hospital outbreak.

The mother’s symptoms began March 5, 2003; she died April 13, 2003. They also sequenced genes from viral isolates cultured from six contacts of the index patient, and all these sequences were identical. To investigate whether there were other strains of the SARS coronavirus in Hong Kong at the time of the outbreak, they sequenced the spike glycoprotein gene from isolates of virus cultured from four other patients with SARS who had had no contact with the index patient. Sequence variations were observed beyond what could be explained by culture-derived artifacts, leading them to conclude that two different SARS strains caused the infections.

"Our data show that since the first reports of SARS in November 2002 in Guangdong province, at least two strains of SARS coronavirus have emerged," the authors reported. "It is epidemiologically significant that even by mid-March 2003, these two strains of the SARS coronavirus had already been found in patients in Hong Kong. This observation means that there was more than one source of infection present at the beginning of the SARS epidemic in Hong Kong. Therefore, even if there had been no outbreak at the Metro-pole Hotel, SARS would probably have broken out eventually in Hong Kong."