The advances, by the University of Hong Kong, are considered an important step in slowing the spread of severe acute respiratory syndrome, or SARS, and bring scientists closer to determining how best to treat it.
The progress comes less than a week after the World Health Organization pulled together the talent from 11 laboratories around the world in an unprecedented collaboration to hunt down the disease.
"We can be relatively sure that we have now found the causative agent," said Dr. Klaus Stohr, a WHO virologist who is coordinating the global laboratory network.
"We know what it is it. It is the SARS virus. But, to which virus family it belongs, we don't know yet," he added.
Some researchers believe it is a new type of paramyxovirus, but studies from other labs suggest it may belong to another virus family.
The virus, isolated from the lung tissue of a patient who died from SARS, is the basis for the diagnostic test, which Stohr said could be available to labs by the end of next week and in the hands of hospital doctors shortly afterward.
The test would make it possible for doctors to quickly weed out and isolate patients with the new disease.
The development of the diagnostic test was announced Friday, but experts were cautious because the results had not been confirmed by further experiments. By Saturday its accuracy had been verified in eight more patients and more details were released.
"The consistency of these findings indicates that the test is reliably identifying cases of SARS infection," the WHO said.
SARS has made 386 people around the world ill and killed 11 people in the past three weeks, according to WHO figures. Experts suspect it is linked to an earlier outbreak of an unidentified disease in China, where officials say 305 people have fallen ill and five have died.
But Hong Kong's Hospital Authority said Sunday that an 80-year-old man with SARS had died this weekend, becoming the eighth fatality here, and another 25 people have been sickened for a total of 242.
And Canadian officials said Saturday they were investigating a third death from what they suspect was SARS.
Hong Kong remains the most seriously affected area, with more than half the total cases. Vietnam and Singapore have also been hit hard. The United States has reported 22 suspected cases, according to the latest WHO figures.
The State Department on Saturday warned Americans not to travel to Vietnam, one of the first countries affected.
In Hong Kong, three grade schools with sick students were closed for disinfection. Singapore, meanwhile, said it would empty one of its main hospitals and dedicate it to coping with the disease.
"This spectacular achievement is an example of what the world can do when the intellectual resources of nations around the world are focused on a single problem," Stohr said. "This rapid advance is fueling the hope that SARS can and will be contained."
By Emma Ross