The death rate from severe acute respiratory syndrome has increased sharply since the epidemic began, and the new lung infection is now killing about 15 percent of victims overall, the World Health Organization concluded yesterday.
It remains unclear whether the death rate is increasing as the disease spreads, or whether the true death rate is simply emerging as more data become available. In either case, the relatively high death rate underscores the seriousness of the threat, WHO said.
"This is a disease that has a high case-fatality rate," said Klaus Stohr, WHO's top SARS scientist. "The case-fatality rate that we're seeing emphasizes even further the need to act decisively now."
According to the new calculations, SARS kills less than 1 percent of those 24 or younger, but the death rate jumps to 6 percent at ages 25 to 44, to 15 percent for those 45 to 64 and to more than 50 percent for those 65 and older, WHO said.
That means SARS has a death rate far higher than those of most other respiratory infections. The typical flu season has a death rate of less than 1 percent. The devastating Spanish flu of 1918 to 1919 had a death rate of less than 3 percent.
SARS does not appear to be as contagious as the flu, but it is the first dangerous new disease that can be spread directly from one person to another to emerge in decades, and it remains untreatable.
"We don't want to add to panic," Stohr said. "But we want to show that this disease should not be underestimated."
The new estimates are based on an analysis of the most recent data from everywhere SARS has erupted -- Canada, China, Singapore, Vietnam and Hong Kong -- and represent the first attempt to produce a comprehensive picture of the disease's mortality, WHO said. An independent estimate released the day before in the Lancet medical journal, which looked only at Hong Kong, projected that the mortality rate there could eventually hit about 20 percent.
Meanwhile, the U.S. Centers for Disease Control and Prevention, under intense pressure from WHO, said yesterday that it will begin reporting more detailed information on SARS cases as early as today.
The CDC has refused to release specific data on the 63 probable SARS cases it has been tracking, notably how and where those patients were infected, whether they spread SARS to others, their ages, medical history and travel patterns.
The Atlanta-based agency has instead released state-by-state figures on suspected and probable cases and has characterized them only in general terms. WHO experts said that without the more detailed information, it becomes far more difficult, if not impossible, to monitor the worldwide trends of the epidemic.
"We need to make sure we know where disease is occurring and that disease is not exported from those sites to other countries," said David L. Heymann, who heads WHO's communicable diseases division.
No one has suggested that the United States is "exporting" SARS cases, but the information gleaned here could help scientists track the movement of the virus and better understand how it behaves.
If federal health officials were to learn, for instance, that a patient in the United States had likely contracted the illness in a country that has not been identified as a SARS hot spot, that could be an early warning of another problem area. Similarly, if new cases arise in individuals who recently traveled to Canada or Vietnam, that would suggest that those countries have not put the outbreak behind them.
"Infectious diseases know and respect no borders," Heymann told members of a House oversight panel at a hearing yesterday. "Information provided early can help nations stop outbreaks."
WHO initially estimated that the death rate from SARS was less than 4 percent. The estimate climbed to a range of 6 percent to 10 percent in recent weeks as the toll mounted.
WHO said the mortality rate ranges from a low of 8 percent in Hanoi, the site of one of the earliest outbreaks, to a high of 15 percent to 19 percent in Canada. Hong Kong currently has a death rate of 11 percent to 17 percent, compared with 13 percent to 15 percent in Singapore and 5 percent to 13 percent in China.
The variations among countries, and the rising death rate overall, may be the result of the disease hitting older people during later outbreaks. It could also be the result of the disease producing a more lethal form of the illness in some places, such as Hong Kong, or simply that enough time has passed to get a more accurate estimate, Stohr said.
"Overall, the case-fatality rate has increased globally. That we know. There appears to be an evolution over time," Stohr said.
The death rate from SARS has been the focus of intense debate. Initially, WHO calculated the death rate by dividing the number of deaths by the number of cases. But some experts said that underestimated the death rate because it failed to take into consideration that many people who were hospitalized would not survive. WHO defended its previous calculations, saying the earlier method was the only one available in the early days of the epidemic.
Christl A. Donnelly, an epidemiologist at Imperial College in London who worked on the Lancet study, said she was pleased that WHO's estimates were coming into line with her group's. She said the findings emphasize the need to identify infected people as soon possible so they can be isolated before they can transmit the virus to anyone else.
"You need to avoid infections as soon as possible. If you can get people who are infected and show the onset of symptoms, you have to get them out of the community to reduce the risk of further transmission," Donnelly said.