This week, medical experts are looking back on the emergence of a mysterious new disease that originated in southern China and spread to more than 30 countries.

One year has passed since a new virus, now known as Severe Acute Respiratory Syndrome, started spreading among humans. Experts trace the first SARS case to a man in rural southern China who fell ill last November. From there, SARS spread to more than 8,000 people worldwide and caused an estimated 700 deaths.

The disease spread first in China's Guangdong province, where doctors reported an unusual and fast spreading viral pneumonia in December. By late February the SARS outbreak had spilled over into neighboring Hong Kong.

Dr. K.Y. Yuen at the University of Hong Kong was one of the first scientists to isolate the virus.

"The peak of the epidemic from the Guangzhou experience was between January to March," he said. "The border is a very important point. Hong Kong had a delay of two months."

Patients with the disease at first suffered from a flu-like illness with high fever, chills and muscle aches. But instead of recovering, many developed pneumonia, often so severe that they required help in breathing.

The illness sparked international headlines in March when almost an entire hospital ward of patients fell ill within days of each other in Hong Kong.

Days later, the disease had spread to Vietnam and Canada - carried by travelers from Hong Kong, and eventually to 30 other countries.

Part of the problem with containing the disease was that mainland officials revealed almost nothing about it to neighboring countries. It took pressure from the World Health Organization to get Beijing to release crucial epidemiological information.

Dr. Yuen says Hong Kong health officials and scientists now communicate regularly with their counterparts in mainland China.

"We have been collaborating with a lot of our colleagues in China in terms of academic collaborations," said Dr. Yuen. "But of course at the governmental level they are now starting more and more dialogue. They now exchange data on notifiable infectious disease and also infectious diseases."

The SARS outbreak was contained in June in part by quarantines of those exposed to the disease and international warnings to avoid traveling to infected areas.

The spread of the new virus highlighted how vulnerable communities are to infectious disease in a time of mass travel between cities and regions. It also showed the need for greater international cooperation on health issues.

There still is no cure or vaccine for SARS.