LONDON – The first major study of SARS trends estimates that about 20 percent of the people hospitalized with the disease in Hong Kong are dying from it, and that more than half of those over 60 die.
The findings are similar to earlier, cruder estimates for Hong Kong, one of the areas hardest-hit by SARS. However, experts warn that the figures do not reflect the chances of an average person anywhere dying from a bout of SARS once it is contracted.
The average age of the SARS patients in the study — those hospitalized in Hong Kong — is 50, and disease experts generally agree that the virus is much more deadly in people over 60.
Nearly 200 of the more than 1,600 people believed to have the respiratory disease in Hong Kong have died.
Led by Roy Anderson, regarded as one of the world’s leading infectious disease experts, the new research is the latest in a weekslong debate about the true death rate for SARS.
The rate has risen sharply from below 5 percent in the weeks that SARS was first spreading around the globe.
Worldwide, the World Health Organization (news – web sites), which is leading the effort to stop SARS’ spread, says the death rate ranges from 6 percent to 10 percent, depending on location. The U.S. Centers for Disease Control and Prevention puts the rate at 6.6 percent.
One WHO official noted that the death rate is lower in places where the outbreak has ended or is nearing an end. “We know that in a real situation where the outbreak has completed itself from beginning to end — in Hanoi, Vietnam — they had an 8 percent case fatality rate,” said WHO spokesman Dick Thompson.
And in Canada, where patients have been older, the death rate is 15 percent, he said.
“What we do see is that in people under 40 the death rate is generally lower and in people over 60 the numbers are much higher,” Thompson said.
The Lancet study, conducted by scientists at Imperial College in London, the University of Hong Kong and the Hong Kong health authorities, estimated that the death rate could be as high as 55 percent in people over the age of 60.
In younger people — those under 60 — the death rate could be as low as 6.8 percent, the study found.
“That’s sadly still very high for a respiratory infection,” said Anderson, a professor of infectious disease epidemiology at London’s Imperial College. “In other common respiratory infections it is much less than 1 percent in the vulnerable elderly.”
The former head of the U.S. Centers for Disease Control and Prevention said quibbling over the death rate “really doesn’t matter one whit.”
“It’s a serious illness, whether it’s 5 percent or 25 percent,” said Dr. Jeffrey Koplan, now vice president of academic health affairs at Emory University in Atlanta. “It’s much higher than a cold or influenza or most other infectious diseases that we commonly encounter.”
Officials with the CDC and WHO would not comment immediately on the new research.
Calculating the death rate has been a sore point for the world’s epidemiologists. Two methods dominate among scientists: The method used by the WHO and CDC is to divide the total number of deaths by the total number of SARS cases. The second approach involves dividing the deaths by the total of those recovered plus those who died.
Anderson said both those methods are deeply flawed and underestimate the death rate because they ignore the fate of people who are still ill.
His method involves sophisticated mathematical calculations to estimate how many of those who are ill will eventually die.
He acknowledged his method still has the drawback of not knowing how many people are infected with SARS but do not get sick enough for the infection to be noticed.
“This is the death rate based on those who have been admitted to hospital, and they tend to be the more severe end of the cases,” Anderson said.
The Lancet study, based on 1,425 SARS cases in Hong Kong up to April 28, also found that the maximum incubation period — the time it takes between getting infected and becoming ill — may be as long as 14 days.
Quarantine measures have been based on a maximum incubation period of 10 days.
If the incubation period is truly longer than 10 days, people who are being quarantined because they have been in close contact with a SARS patient may not be in isolation long enough.
“The article does raise the caution that maybe we need to move the curve out a little bit by four days and that’s well worth further study,” Koplan said.
WHO said it is possible that the incubation period could be longer than 10 days because the U.N. agency calculates it starting from the last day a person was exposed to SARS.