The head of the U.S. Centers for Disease Control and Prevention said a number of tests had revealed traces of a form of microbe known as a coronavirus in the tissue of people infected with the unidentified disease.
"There's very strong evidence to support coronavirus" as the cause, said CDC director Dr. Julie Gerberding at a news conference. However, she cautioned that more testing is needed before experts can be certain.
Many different viruses can cause colds, including three different varieties of the coronavirus. Until now, in fact, the cold is the only human ailment known to be caused by coronaviruses, but the CDC said the culprit in the Asian outbreak appears to be genetically different and probably represents a fourth type.
Just what that means for treating severe acute respiratory syndrome, SARS, which has sickened 456 and killed 17 since Feb. 1, is unclear. There are no certain treatments for colds caused by this or any other virus. Nevertheless, Gerberding said the Defense
Department will test the virus against all known antiviral drugs to see if any work.
Researchers worry that any virus they find in patients may be an innocent bystander.
Among the bits of evidence suggesting the new coronavirus really is the cause is the discovery that victims develop an immune system response to it during the course of their illness.
The illness first gained attention in Hong Kong, Singapore and Vietnam, where it has spread among health workers in hospitals. Health authorities say it appears to spread from close contact, primarily through nasal fluids by coughing or sneezing.
The Geneva-based World Health Organization issued a worldwide travel alert March 15 warning people to watch for symptoms after traveling to places where the disease had appeared. The WHO also got its network of 11 labs around the world working to find the cause and treatment of the disease.
Gerberding's announcement followed comments earlier Monday from a WHO scientist who said for the first time that coronavirus was a possible cause. But the virologist, Dr. Klaus Stohr, continued to give more weight to a different virus, described by WHO officials earlier, the paramyxovirus.
Gerberding said her researchers had not found that virus in their tissue samples.
Meanwhile, fears of the disease seemed to spread in some Asian Centers.
Singapore's government moved to put the brakes on the illness, reports CBS News Radio Correspondent Christopher Glenn. The Health Minister, invoking the city-state's Infectious Diseases Act for the first time, has ordered about 740 people who may have been exposed to the illness to stay home for ten days.
Hong Kong officials met to draw up health guidelines for everything from restaurants to bus systems in an attempt to slow its spread.
Hong Kong's health secretary, Dr. Yeoh Eng-kiong, called SARS "a really very alarming disease," the likes of which Hong Kong has never seen.
On Sunday, the territory's top health official was hospitalized with the respiratory symptoms indicative of the disease, which merely added to the anxiety.
"I think it's spreading very quickly," said Lisa Fung, a masked 44-year-old worker at a domestic help recruitment agency. "Even William Ho has got it and he hasn't had to go treat the patients."
Many residents wore surgical masks around the city, hoping to avoid infection.
Health authorities suspect SARS is linked with an earlier atypical pneumonia outbreak in mainland China's Guangdong province that killed five people and sickened 305. A WHO team that arrived over the weekend in Beijing said Monday it was analyzing the Chinese cases in the scramble to unravel the disease.
Some of the sickest Hong Kong patients were receiving injections of antibodies obtained from victims who have recovered and their initial responses appeared good, Yeoh said.