The coronavirus present in those with SARS is, as suspected, new to humans, two research teams reported in the New England Journal of Medicine.
The researchers proposed naming the virus after Dr. Carlo Urbani, the World Health Organization doctor who died of SARS last month after treating one of the first patients infected with the virus in Vietnam.
The finding means that doctors can now concentrate on developing a simple test for the virus that will tell them right away whether a patient has SARS. The U.S. Centers for Disease Control and Prevention is currently refining diagnostics tests that it has developed in collaboration with the WHO and other laboratories.
CDC researchers are also working to sequence the DNA of the virus, which will give them a better idea of where it came from and what it is.
SARS, which was spread around the world by travelers, has killed an estimated 110 people and over 2,700 have been infected. Despite the continued increase, authorities in the United States and many other affected countries believe they have the infection under control.
In China, Hong Kong and Singapore, areas hardest hit by the virus, the picture is less clear.
Singapore Thursday placed a quarantine on arriving foreign workers and took dramatic measures to enforce quarantine orders on hundreds of people suspected of exposure to SARS, including mounting "Webcams" in homes and threatening to use electronic wrist bands.
Hong Kong said Thursday it will quarantine for up to 10 days anyone who resides with a confirmed SARS patient, in a tough measure to halt the spread of a disease.
Hong Kong Health Secretary Dr. Yeoh Eng-kiong said the quarantine measure was going "one step further to help contain the spread of the disease," but that the decision had been difficult because of a divergence of views on restricting people's freedoms. Health Director Dr. Margaret Chan said police will make sure people don't violate the quarantine by making unannounced visits to their homes.
"This is not a foolproof system," Chan told a news conference. "The key is based on self-regulation plus checks on compliance."
Anyone who does not comply with the order will be removed to designated places for isolation, and they could be fined or imprisoned, Chan said.
Hong Kong health officials declined to predict how soon they can bring SARS under control or how many people will be affected by the new restrictions. The Hong Kong health care system is being taxed to its limits by the SARS crisis.
A quarter of Hong Kong's 1,000 cases of SARS are health workers.
"I am afraid that if more hospital staff get infected, the entire health care system would collapse," Peter Wong, a spokesman for three major nurse unions, told a news conference.
He said Hong Kong government hospitals were not providing staff with adequate protective gear.
The government said another three people died of SARS Thursday, bringing the toll to 30, and officials feared the illness could spread further through the city's crowded apartment towers.