The death rate for Sars could be significantly higher than previously thought, according to an British expert's study into the pneumonia-like virus.
Travellers are being informed about Sars
The research by Professor Roy Anderson, due to be published in a medical journal next week, is expected to say the virus could kill between 8% and 15% - or one in seven - of those infected.
The World Health Organization (WHO) had predicted a death rate of 5% to 6% and said the virus could be beaten if countries worked together to stop it spreading.
A WHO spokesman said Professor Anderson was a top class professional and his findings were probably accurate.
Latest figures show Sars has infected an estimated 4,649 people in 26 countries around the world. So far more than 274 people have died, with most sufferers making a full recovery.
Higher death rates
Professor Anderson, of Imperial College, London, who is one of the world's leading authorities on infectious diseases, told the BBC: "If one looks carefully at the WHO figures on mortality and recovery rates, it is running, unfortunately, at 10%."
The new research was based on the study of the 1,400 or so cases in Hong Kong.
Prof Anderson analysed the spread of Sars in Hong Kong, where 121 people have died so far.
He calculated that between 8% and 15% of those who contracted Sars would die.
His research also found Sars remained infectious much longer than other viruses.
But Prof Anderson told the BBC that media speculation about Sars had exaggerated the problem facing the world.
He said the higher mortality rate was not the most important issue as so many other health factors could influence a patients' death.
Prof Anderson said: "If this was a highly transmissible agent that was spreading like wildfire then of course there would be huge cause for concern, but it is not.
"It appears to be contained, certainly in developed countries, by very good containment and monitoring practices.
"The concerns lie in the large populous regions of the world: China, India, Indonesia, where the disease reporting systems are limited and it is much less clear to work out what is going on there.
"This just reminds us that we are a globally mixing community and what happens in one corner influences us all."
On Saturday, Dick Thompson, a spokesman for the WHO's communicable disease section, said: "We have not seen the report so we could not comment except to say that this is a top class professional and any figure he commits himself to is likely to be as close as possible to accurate."
WHO executive director of communicable diseases, David Heymann, said on Friday he believed the disease could be stopped if everyone worked together.
KNOWN DEATH TOLL
Hong Kong: 121
Source: WHO/ local health authorities
"What is important is for all countries to participate and to help prevent it getting in a place where it would be very difficult to stop it," said Dr Heymann.
Of the 26 countries that had seen Sars cases, 23 have contained it well, according to the WHO.
Officials have also taken comfort that it has not spread as easily as other viruses, such as influenza.
There have been six probable cases of the virus in the UK, but no deaths.
A group of school children from Cheshire returned home early from a cultural exchange visit to Beijing on Saturday.
Two members of staff and 21 youngsters from Knutsford High School in Knutsford, had been due to return from their cultural exchange visit to Beijing on Sunday but came home a day early.