Government agencies, university labs and private companies are rushing to develop highly sensitive tests that will seek out the newly discovered virus and confidently enable a diagnosis of severe acute respiratory syndrome, once their accuracy has been proven.
The tests, which search for viral genes in victims' nasal secretions and other samples, are likely to work only in the early stages of the disease, before the body defeats the virus, removing all traces it existed.
About three dozen Americans have probable cases of SARS according to the definition of the deadly flu-like disease followed by the rest of the world, federal officials said yesterday.
In all, the CDC lists 208 Americans from 34 states as probable or suspected SARS cases. However, only 35 of them meet the definition for probable cases of the disease set by the World Health Organization.
The tests will be used cautiously at first, while developers work to prove that they pinpoint the virus in infected people without sending up frequent false alarms in the healthy. Until this accuracy is known, "we will be loath to say someone doesn't have SARS on the basis of the test," CDC head Dr. Julie Gerberding said yesterday.
Nevertheless, experts say they hope the tests will soon enable doctors and public health officials to distinguish whether people with fresh symptoms have SARS or other look-alike ills, such as bad colds and flu. Then they can more knowledgeably decide whether the patients need elaborate infection-control precautions in hospitals and whether their families, co-workers and friends should be watched for symptoms and perhaps quarantined to prevent passing the virus to others.
"We could basically target our prevention at those who truly have SARS," said Dr. Elizabeth Koch, an epidemiologist in the Ohio Department of Health.
Dr. James Hughes, head of the CDC's National Center for Infectious Diseases, said its test will be sent to about 100 state, city and federal health labs within two weeks, perhaps as soon as the end of next week. The labs, in turn, will test samples sent to them by hospitals with suspected SARS cases.
The CDC test has been tried on 300 randomly selected specimens, all with negative results, and on many of the 208 suspected U.S. cases from 34 states. Hughes said the results suggest the test is accurate enough for wide distribution, although it was created before scientists knew the full genetic code of the SARS virus.
On suspected cases, "we have a lot of negative results using it here and a few positives," he said. "It looks like it works."
Dr. David Freedman, head of the travelers' health clinic at the University of Alabama in Birmingham, said hospitals are eager to learn whether people with suspicious symptoms are infected.
"If a probable case comes into the hospital, every nurse, every doctor, every janitor has to have gowns and gloves and masks to go into [the patient's] room, which has to have negative pressure ventilation," he said. "It's a big thing that really impacts on hospital expenses."
Researchers say they are dazzled by the speed with which the virus' secrets have been unlocked and shared, enabling far-flung scientists to try out each other's tests or create their own.
"What is remarkable is the way the information is coming out so fast," said microbiologist Frederick Nolte of Emory University. "Everything is in the public domain that is needed to put together a test for the virus."
Nolte, for instance, is using material developed by the Bernhard-Nocht Institute for Tropical Medicine in Hamburg, Germany, to help create a fast SARS test for use at his university hospital.
Meanwhile, the Hamburg institute is circulating its test to a network of labs in 10 countries so scientists can judge how reliably it finds small amounts of the virus, especially among people in the earliest stages of infection. The World Health Organization cautioned yesterday against relying too heavily on this test, because it might not be powerful enough to catch everyone with the virus.
All of these tests are based on a standard laboratory procedure called PCR, or polymerase chain reaction, which is used to diagnose dozens of other infections. The process can find bits of genetic material that are unique to the virus, then reproduce them in large quantities for easy identification, yielding an answer in a day or less.
Heiner Dreismann, president of Roche Molecular Systems, said his company hopes to have a PCR test for SARS finished within eight weeks. It has set up a network of doctors in Canada, Hong Kong and Singapore who will quickly do the needed experiments to prove its accuracy.
Ordinarily, the Food and Drug Administration takes a year or longer to review such data. But in this case, the agency is expected to approve tests in days or even hours if they appear reliable.