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Experts Recommend New Testing Guidelines for SARS - 2003-10-22

Global public health experts are proposing ways to improve testing for the respiratory disease SARS so only true cases are diagnosed and not confused with diseases with similar symptoms, like influenza. The specialists want to begin by dividing the world into three zones according to the degree of SARS risk.

As the winter influenza and pneumonia season approaches in the Northern Hemisphere, there could soon be a large number of people with a respiratory ailment with symptoms like SARS. To prevent the need for SARS tests in each case, a team of public health specialists meeting in Geneva proposes administering them only where the likelihood of a SARS resurgence is high.

To determine where testing should occur, the head of the World Health Organization's laboratory group, Australian physician John MacKenzie, says he and his colleagues propose dividing the world into three regions. The first would include areas at the center of the epidemic, mainly China and Hong Kong, where the virus could occur again. The second would contain areas where the virus has infected people but is not active now, such as Singapore and Toronto, Canada. The third zone would be everywhere else.

"In places where we don't normally see the virus, the chances of it being the agent are really very small indeed. So our suggestion is that we should not be testing routinely people who have atypical pneumonia for SARS," explained Dr. John MacKenzie.

In the least-affected areas, SARS testing would occur only as a last resort, when a cluster of cases occurs and antibiotics do not work. These same guidelines would apply to the second group of areas, but health care workers there should be a little more likely to test for SARS.

Speaking by telephone from Geneva, Dr. MacKenzie admitted that the strategy might miss the first few SARS cases in an area of low risk. But he pointed out that the system is a trade off to prevent overwhelming laboratories in these regions.

"We have to be able to test, but we also have to be able to manage the number of tests, given the possibility that once we get into the influenza season, we will have such a large number of cases of atypical pneumonia that the laboratories will be flooded with specimens," he said. "So what we're trying to put together is the best risk system."

The experts also want to impose an international double testing plan for SARS. The scientist who discovered the SARS virus six months ago, Malik Peiris of Hong Kong University, explained that a repeat test by a different laboratory would help reduce the number of cases where flu or pneumonia patients are incorrectly diagnosed with SARS.

"It is inevitable that there will be false positive results," he said. "So what we discussed today was a system where the laboratory will take a number of steps to make sure that the result is accurate and it will be referred to a second laboratory to make sure that the crosschecking system is in place."

A problem hindering accurate SARS testing is the lack of enough blood samples from patients that all laboratories can use to compare test results. The experts say they are considering recalling some former SARS patients who still have antibodies to the virus to donate blood so a large specimen pool can be amassed.

The experts met at the World Health Organization in Geneva, which is expected to publish the new testing guidelines in about one week.