Singapore officials say a man with Severe Acute Respiratory Syndrome probably contracted the disease in the medical research laboratory where he worked. Regional airports, hospitals and universities are stepping up SARS-monitoring efforts.

Health officials in Singapore said Wednesday the medical laboratory has been temporarily closed as experts investigate how a lab worker contracted SARS.

"We would have to look at where the measures in the laboratory may have failed and what kind of safety measures we would introduce to ensure this kind of incident does not occur again," said Balaji Sadasivan, Singapore's minister for health.

The infected man, who had not been working with the SARS virus, is recovering in a hospital from fever and flu-like symptoms. Doctors say he has not developed atypical pneumonia, one of the most deadly effects of SARS.

Peter Cordingley, the World Health Organization spokesman in Asia, says that while the isolated case is not a threat to the public, it is still a concern.

We consider it a SARS case but we don't consider it a typical SARS case because his lungs are not infected," Mr. Cordingley told Hong Kong Cable Television on Wednesday. "But the bottom line is that he does have [the] SARS virus."

The Singapore case comes four months after the city declared itself SARS-free. It is also the first case in Asia in more than two months and has sparked fears the region could face a fresh outbreak of the disease.

The head of Hong Kong's public hospital system says he is very concerned about the case and has stepped up SARS surveillance measures.

Hospital Authority Chief Executive William Ho says Hong Kong has adopted a "SARS alert" similar to that recommended by the World Health Organization. The system requires hospitals to inform the health department if two or more workers or patients in a ward contract a respiratory illness within 10 days of one another.

Dr. Ho said hospitals might be asked to set up fever clinics to monitor and isolate patients with high temperatures. Laboratories in Hong Kong doing SARS research are also examining safety measures.

When SARS first spread from China to Hong Kong, Vietnam and 30 other countries in March and April, the travel industry in Asia suffered a sharp decline. Retail sales also plunged, and stock markets sank in many cities.

On Wednesday, Hong Kong's main share index fell more than two percent in what traders called panic selling prompted by the new SARS case. Singapore's main share index has fallen about three percent since Tuesday.