"It would be distinctly unusual for a respiratory disease spread this way to all of a sudden just disappear," said Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases.
"We have not yet begun to see the worst of SARS," predicted Michael Osterholm, an infectious disease expert at the University of Minnesota.
Osterholm predicted more cases would appear next winter, spread from developing parts of the world where diseases are not well contained.
"If this projection is correct, we have every reason to believe that this disease may show up in multiple U.S. cities as we continue to travel around the world in unprecedented numbers and speed," he said.
The World Health Organization extended its SARS travel warning to all of Taiwan on Wednesday, and even as the disease retreated in many other places.
Taiwan reported 35 new SARS cases and said its epidemic has yet to peak. The U.N. health agency said it was advising travelers to avoid the whole island, extending advice that previously only related to the capital, Taipei.
With 418 cases, including 52 deaths, Taiwan has the world's third-highest toll of severe acute respiratory syndrome after China and Hong Kong. Hong Kong has displayed the highest per capita toll to date
In Taiwan, focus was shifting from Taipei in the north, where SARS closed two hospitals last month, to Kaohsiung in the south, where two hospitals have also reported outbreaks. Across the island, more than 12,000 people were still under quarantine.
"The coming week could see a peak in SARS cases in the south," said Center for Disease Control chief Su Yi-jen.
China reported 12 new cases of infection on Wednesday and Hong Kong reported one. They also announced only two deaths each — among the lowest daily tolls since the disease was first reported in southern Guangdong province in November.
Taking no chances, Chinese President Hu Jintao has had tests to make sure he isn't infected with SARS when he meets President Bush and other G-8 leaders next month in France, a senior Chinese official said.
WHO experts fear that summer floods could push water laced with sewage into homes and spread infection.
The SARS virus doesn't appear to be transmitted by water, but can survive for days in feces, which might be spread by overflowing sewage, said Bob Dietz, a WHO spokesman in Beijing.
"We see this as a potential threat, something to beware of," Dietz said. "SARS could rear up again."
SARS has killed 296 people on China's mainland and infected more than 5,200.
Although the crisis seems to be waning, Chinese officials say tough public health measures will remain in place, and Hong Kong began checking China-bound train passengers for fever — a key symptom.
On Wednesday police said they had detained a man with SARS who broke a quarantine order and fled twice from a hospital in Tanghe, a city in Henan province in central China.
In extreme cases, China's quarantine laws can carry a death sentence for violators. Police said the man hasn't been formally charged and it wasn't clear what penalty he might face.
China's state media reported the government will give $12.1 million in aid to airlines and other travel businesses in hopes of limiting the economic damage from the disease.
Some hotels in Beijing and Shanghai have closed temporarily and many restaurants have shut as customers afraid of contracting the disease stay home.
In other developments: