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Death rate rising { April 25 2003 } Original Source Link: (May no longer be active)
http://www.washingtonpost.com/wp-dyn/articles/A35146-2003Apr24.htmlhttp://www.washingtonpost.com/wp-dyn/articles/A35146-2003Apr24.html
Death Rate for Global Outbreak Rising
By Shankar Vedantam and Rob Stein
Washington Post Staff Writers
Friday, April 25, 2003; Page A01
The death rate for the worldwide outbreak of severe acute respiratory syndrome, which has fluctuated for months, has recently begun what looks like an ominous rise.
As of yesterday, 263 people have died of SARS worldwide. Although the rate of deaths from the strange new illness initially hovered as low as 3 percent, it has soared to twice as much in recent days, prompting questions about whether the virus is growing more lethal, spreading faster or striking more vulnerable people.
The questions are easier to ask than answer, because the epidemic is still in its early stages: The virus could indeed be killing more people than it did a few weeks ago, researchers say, possibly because of some unknown mutation that has made it more deadly. Equally likely, however, the virus's lethality may not be changing at all -- and the changing numbers may simply reflect statistical aberrations or even changed definitions of what constitutes a case of the disease.
The death rate "has gone from 3.5 and 4 percent, and is now between 5.9 and 6 percent," said Julie Gerberding, director of the U.S. Centers for Disease Control and Prevention, yesterday. "The fact that it is changing is not at all surprising, given that the case definition is changing. . . . Different countries are using different definitions."
Still, the rising numbers are cause for concern for three reasons. First, the current -- higher -- death rate is statistically more reliable than the previous -- lower -- estimates.
Second, as hospitals learn to cope with the outbreak and doctors find ways to treat or stabilize patients, the death rate ought to head down, not up.
Finally, large numbers of cases so far, especially in places such as Hong Kong and Singapore, have involved hospital workers, who tend to be younger and healthier. As the SARS virus has spread to the general population in some places, it may strike more vulnerable elderly people and increase in lethality.
Statistics in Hong Kong show that the death rate among people younger than 55 is 3.6 percent. For patients between 65 and 75, it is 18.9 percent. For those older than 75, the death rate is 28.6 percent.
In Canada, the death rate yesterday as reported by the World Health Organization was 10.71 percent, one of the highest in the world, with most of the cases in the Toronto area. The number was based on WHO's count of 15 deaths and 140 cases.
"In Canada, the death rate seems to be very high," said David Brandling-Bennett, deputy director of the Pan American Health Organization in Washington, WHO's regional office. "One wouldn't expect to see higher death rates in Canada -- it may depend on the intensity of the exposure. The more viral particles you get, the more severe the disease."
However, Andrew Simor, who has been treating SARS cases in Toronto, argued that the death rate in Canada is no higher than elsewhere. He said that communication lags meant that the WHO statistics are not always based on the latest figures: "We have 16 deaths out of 270 cases," he said, for a death rate of about 5.93 percent.
Still, Simor acknowledged, "We do have a sicker population," in part because a larger number of elderly people have been exposed. "Fifteen percent end up on a ventilator. . . . The older you are, the more likely you are to run into serious disease."
Such confusion and uncertainty is common in the early days of a worldwide epidemic such as SARS. Doctors do not yet have a practical laboratory test for the virus, meaning that some people with garden-variety influenza are probably being counted as SARS patients, while others, who really have the illness, are being left out of the calculations, said Marc Lipsitch, an epidemiologist at Harvard's School of Public Health.
Additionally, countries such as China, with the largest number of cases in the world, started out trying to mislead WHO about the true extent of SARS, placing national prestige and economic concerns over public health.
Finally, epidemiologists say that the overall number of SARS cases in the world has only recently soared to the size necessary to draw meaningful statistical conclusions about the death rate, which is calculated by dividing the number of deaths by the number of people infected.
Yesterday's statistics, for example, counted 4,439 cases of SARS and 263 deaths worldwide, for a death rate of 5.92 percent.
Lipsitch said a larger number of cases yields a more reliable rate because it reduces the possibility of chance variations. With 40 SARS deaths among any 1,000 cases, the calculated death rate would be 4 percent, but statistically, it is equally likely that in the next 1,000 cases, the number of deaths will be anywhere from 29 to 54 -- yielding rates of 2.9 percent to 5.4 percent, he said. By contrast, with 4 deaths in just 100 cases, the rate for the next 100 cases is statistically likely to be anywhere from 1.1 percent to 9.9 percent.
Only two places, mainland China and Hong Kong, have enough cases to calculate meaningful local death rates: China's stands at 4.54 percent, while Hong Kong is at 7.32 percent.
One thing that worries health officials about SARS is that so far, it seems to be considerably more deadly than influenza, another major respiratory disease that has long afflicted humanity. SARS is the first life-threatening new disease to emerge in decades that can be spread from one person to another by casual contact.
Reliable death rates are available for the flu. In a typical year, it is usually below 1 percent. The Spanish flu pandemic of 1918-19 had a death rate estimated to have been 2 percent. It, however, killed perhaps 25 million people worldwide because it quickly swept the globe and infected millions.
"What made it such a big killer was that so many people were infected," said Stephen S. Morse, director of the Center for Public Health Preparedness at the Mailman School of Public Health of Columbia University. "When you have such a large numerator, then you can still have a tremendous impact."
The actual mortality rate from SARS is likely to be higher or lower than the 6 percent rate that is currently estimated. It may turn out that there are a large number of people who become infected but never fall ill. If that is the case, then the mortality rate will be much lower.
"We don't know what the true denominator is. We don't know the true number of actual SARS cases. So I think it's a safe assumption that it's going to change," Morse said.
The transmissibility of a disease is another key factor in determining how much of a threat it poses. Some diseases have high mortality rates but are not easily spread, so the overall number of people who die is low. That is the case with Ebola, for example, which has a mortality rate of 70 percent to 95 percent but does not spread easily.
© 2003 The Washington Post Company
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