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Only 40% of Suspected SARS Cases Show Presence of Virus in New Study

By Lawrence K. Altman

THE NEW YORK TIMES -- Canada’s main virology laboratory has found the SARS virus in only 40 percent of probable and suspect cases of SARS, or severe acute respiratory syndrome, a surprisingly low rate that puzzles the laboratory’s scientific director and other health officials.

Also, for unknown reasons, the proportion of recent cases that are testing positive for the SARS virus is declining and a number of people who are not suspected of having SARS are testing positive, said the director, Dr. Frank Plummer.

Plummer described his team’s findings as “weird.” He said that they had the potential to weaken the link between SARS in Canada and a previously unknown member of the coronavirus family that the World Health Organization announced last week was the cause of SARS.

Plummer emphasized in an interview that he was not challenging the WHO’s conclusion. He said he was “reserving judgment” because it was too early in the course of the investigation of the new disease, which was first detected only five weeks ago, to be certain about many findings without further study and independent confirmation by other laboratories.

On Wednesday, the WHO said it continued to believe that the new coronavirus is the cause of SARS and is following the developments at the National Microbiology Laboratory in Winnipeg, Canada, where Plummer is scientific director. It is one of the 13 laboratories in an international network that the U.N. agency created to investigate SARS.

But Plummer’s data “is troubling and we don’t understand it,” said Dr. Klaus Stoehr, who is scientific director of the WHO’s SARS investigation.

There could be a number of explanations for the low positive test rate, Plummer, Stoehr and other experts said. They include: The coronavirus is not the cause of the disease or is not its sole cause; specimens tested were collected at the wrong stage of the disease or were taken from the wrong part of the body; and flaws in the laboratory testing.

Plummer’s team in Winnipeg has tested about 3,000 specimens from 95 probable and 90 suspect cases in Canada and in Asia. His team identified the SARS virus in about 40 percent of the probable cases and 35 percent of the suspect cases.

Plummer said he was surprised to find the virus in about 20 percent of an additional 250 people who were not suspected of having SARS but who were tested because they had returned to Canada from affected areas in Asia or who had mild symptoms not thought to be SARS.

If the coronavirus “is the whole and only explanation, which is certainly possible, there are a lot of weird things about it,” he said.