Meanwhile, the worldwide death toll from the severe acute respiratory syndrome has now passed the 500 mark. There have been more than 7,000 reported cases of the disease in 29 countries on five continents.
The WHO revision follows the release Wednesday of a study published in the journal The Lancet that found the death rate for SARS patients in Hong Kong is 20 percent, CBC News Online reports.
WHO officials initially said they weren't sure the Hong Kong study could be applied to other areas affected by SARS. But after they reviewed data from a number of other places such as China, Singapore, Hong Kong, Canada and Vietnam, they increased their estimate of the SARS death rate.
The new WHO estimate reveals that SARS patients younger than 24 have the lowest risk of dying. The death rate increases to 6 percent for people aged 25 to 44, 15 percent for people aged 44 to 65, and more than 50 percent for more elderly SARS patients, says CBC News Online.
Researchers say they need to find out why the elderly are so vulnerable to SARS.
In other developments, the WHO issued new SARS travel advisories Thursday, telling people to avoid non-essential travel to Taiwan and the two Chinese provinces of Inner Mongolia and Tianjin.
Travel alerts are already in place for Hong Kong, Beijing and the Chinese provinces of Shanxi and Guangdong, the Associated Press reports.
A travel advisory against Toronto, Canada, was lifted April 30 after WHO officials reviewed the situation there and decided the SARS outbreak had been successfully contained by health authorities.
China remains the SARS hotspot. The country reported six more SARS deaths Thursday, for a total of 225. China also reported eight more SARS cases, increasing the number of people infected there to 1,654.
Next to China, Hong Kong and Taiwan are most affected by SARS. In Hong Kong, the death toll now stands at 208 people. Taiwan has reported 13 SARS deaths so far and 120 probable SARS cases.
Russia reported its first possible SARS case at the same time that Russian officials suspended ticket sales on all flights to mainland China, Taiwan and Hong Kong, BBC News Online reports.
Russians officials planned to meet Thursday to discuss ways to prevent SARS from spreading into the country, which shares a long border with China.
In China, WHO officials are continuing their investigations in the province of Hebei, where the number of SARS cases doubled in a week. It's believed the highly infectious respiratory disease was carried there by a migrant worker who fled Beijing to escape the SARS epidemic in the capital, BBC News Online reports.
Chinese state media report that 120 government officials have been fired for their slow response to the disease's outbreak. The Chinese government has also announced a series of measures meant to reduce the economic impact of SARS.
The government has ordered local officials to ensure that crops are harvested, and to take steps to bolster tourism. But BBC News Online reports those attempts to salvage economic activity are hampered by government measures -- such as road closures and other travel restrictions -- meant to control the spread of SARS.
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