Test to detect virus found inconsistent

By Daniel Yee
Associated Press

ATLANTA — A test developed to detect the SARS virus appears to be far from foolproof in diagnosing the disease.

The Centers for Disease Control and Prevention said this week that about seven of the 13 probable cases of SARS that were tested came up negative.

"The fact that some of our probable SARS cases are not virologically positive is not surprising," said CDC director Dr. Julie Gerberding.

The CDC also said that of 32 cases classified as "suspected" rather than "probable," all came up negative.

Both she and international health officials said there are several reasons why SARS diagnostic tests have been inconsistent.

First, the definition for SARS is broad and may include symptoms similar to illnesses caused by other viruses.

Dr. David Heymann, communicable disease chief for the World Health Organization, said many of the cases being tested aren't severe acute respiratory syndrome, but some other ailment.

In addition, the tests may not yet be sensitive enough and the timing of a test could affect its accuracy, researchers said.

CDC's negative results are similar to those found by a researcher in Canada, who said 60 percent of the probable and suspected SARS cases he tested came up negative.

In addition, Canadian researchers found that about 300 people tested positive who were not thought to have SARS, including some who hadn't traveled to affected areas of Asia but still sought testing.

Those findings are the most troubling, said Dr. Frank Plummer, director general of the Center for Infectious Disease Prevention and Control in Ottawa. It raises a possibility that SARS is not caused by the coronavirus as epidemiologists believe, he said.

"We really need to nail down whether this (coronavirus) is the cause or not, whether coronavirus is the whole story or if something else is going on," Plummer said.

He said one possibility is that an unrelated virus may be circulating through communities the same time as SARS.

But other researchers said there is strong evidence that the coronavirus is the cause of SARS. Although it's possible another infectious agent could be involved, such an agent hasn't been identified, said Brenda Hogue, associate professor of microbiology at Arizona State University.

The CDC and WHO also are strongly convinced that a type of coronavirus — one of the bugs that can cause the common cold — is the cause of SARS.