Health officials around the world are working to halt the spread of Severe Acute Respiratory Syndrome known as SARS. But the sometimes deadly disease that emerged in Asia continues to spread and the World Health Organization reports there are now more than 2,700 suspected cases of SARS worldwide.

Emergency room physician David Pitrolo was watching CNN television before going to work at a hospital in Virginia the morning of March 15. He saw a report on a new epidemic of an unusual pneumonia in Asia before he began his shift. "One of the first patients I saw in that shift had recently returned from Asia, and had symptoms that were, almost fluish-type symptoms," he said. "And with seeing that report, and seeing her presentation and her travel history, we placed the patient in isolation fairly quickly."

Dr. Pitrolo contacted the U.S. Centers for Disease Control and Prevention. CDC tests soon showed Dr. Pitrolo had spotted one of the first cases of SARS in the United States. "The CDC and the World Health Organization, or WHO, had issued a global health alert for SARS that same day," said Dr. Pitrolo. "The global public health system swung into action. The results have been remarkable, according to epidemiologist David Weber at the University of North Carolina School of Public Health. I think it is an extraordinary event in science, that, in the past where it would often take years to find the cause of an infectious disease, we're able to do it, brand new disease, new to human kind, in just a few weeks."

Dr. Weber says such a quick discovery may not happen for every new disease. And CDC director Julie Gerberding cautions that scientists are not yet 100 percent sure that they've found the cause of SARS. But she agrees that progress has been impressive.

Experts say part of the reason for the quick response is the heightened concern about bioterrorism after September 11, 2001, and the anthrax attacks that terrorized the United States. There's no evidence that SARS is a bioterrorist attack. But bioterror money put advanced disease detection tools in the hands of public health officials in the United States.

Ralph Timperi directs the public health laboratory for the eastern U.S. state of Massachusetts. He says bioterror concerns may also have had influence beyond the United States. "I think there's, more recently, been a much better coordination effort out of WHO," he said. "And once again, there may be a relationship to the fear of terrorism."

The WHO has issued its first travel advisory ever in response to SARS. The organization suggests travelers avoid unnecessary trips to Hong Kong and China's Guangdong province.

But the University of North Carolina's David Weber says scientists were concerned about new diseases before September 11. He says when HIV first appeared in the 1980s, doctors realized they needed to pay more attention to emerging diseases. "We've seen a ratcheting-up of the system, but I think there was an appreciation we needed to look at these issues growing throughout the 1990s," he said.

Dr. Weber says what September 11 and the anthrax attacks did was alert politicians and the public to what was already a big issue in the scientific community.

Public health officials in the United States have set up regional networks that, when activated, can monitor patients for symptoms that could indicate a new disease, or a new outbreak.

But Dr. Weber says despite these measures, individual health care workers are still the first line of defense. "I think we've yet to develop a proven surveillance system to detect new diseases and the way we're finding most of them is just an astute clinician, scientist, or laboratory person who says, I'm seeing things that are out of the ordinary," he said.

Once a new health problem has been spotted, Dr. Weber says, the public health system acts very quickly.

The system responded with lightning speed to the emergence of SARS. But drugs or vaccines are nowhere in sight. Ralph Timperi, the public health laboratory director from Massachusetts, says that SARS will probably be with us for a long time. "It will cycle," he said. "You'll have years of more cases, and years of fewer cases. But there's no reason to think it won't be around. The question is, how significant a disease it will be in the long run."

The University of North Carolina's David Weber says it's important to keep SARS in perspective. "Although there's a lot of press, we still have to realize we're working with a relatively small number of cases and deaths compared to many other risks in society, and, in fact, other common infectious diseases," he said.

David Pitrolo, who spotted the SARS case in Virginia, says his patient has recovered. Most do. And scientists will keep looking for new treatments.