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Also, in a report on the outbreak in Singapore, the U.S. Centers for Disease Control and Prevention said five individuals had acted as 'super spreaders' in passing the virus to 144 other people, while 81 percent of infected people did not transmit to anyone else. CDC defined super spreaders as individuals who transmitted SARS to 10 or more other people. Doctors have described super spreaders in other infections such as tuberculosis, rubella and Ebola

Unless the numbers fall drastically, SARS would be among the infectious diseases with the highest death rates. Until now, fatality rates reported by the World Health Organization had ranged from 2 percent, when the epidemic was first detected in March, to 7.2 percent. The new findings come from a statistical analysis of 1,425 patients suspected of having severe acute respiratory syndrome who were admitted to Hong Kong hospitals from Feb. 20 to April 15. Overall, their mortality rate was estimated to be as high as 19.9 percent. The principal authors of the study from Imperial College, the University of Hong Kong, the Chinese University of Hong Kong and the Hong Kong health department said their findings underscored that SARS is a serious threat to the public and that health officials and workers must act to contain it. The authors credited Hong Kong's efforts to reduce the time from the onset of symptoms to the isolating of patients in hospitals as an important step in controlling the disease. Reducing the time did not affect the course of the illness in individual patients, they said, but speeding the isolation process reduced the period when they could transmit the virus to others. The study, said Dr. Michael Osterholm, an expert on infectious disease at the University of Minnesota, 'looks solid and provides an important source of information about the evolving epidemic.' Dr. Klaus Stoehr, the scientific director of the SARS investigation for the World Health Organization, said in an interview that the agency was reviewing the new data and the statistical models used to obtain them. 'The case-fatality rate can be calculated in many ways and can depend on various scenarios,' Stoehr said

Calculating death rates for new diseases like SARS is notoriously difficult for epidemiologists, particularly if there is no definitive diagnostic test, as is the case with SARS. The final death rate will not be known until the epidemic has run its course. Moreover, death rates can vary from one set of patients to another, depending on factors like the amount of virus transmitted, where it entered the body, and the functioning of an individual's immune system. Yesterday, the W.H.O. stood by its 10-day estimate. That figure was determined by reviewing cases in which the patient had a single documented exposure to a known SARS patient in Canada, Europe or Singapore, the agency said. The United States has begun to take steps to patent the SARS virus and its genes because if others patent them, Dr. Julie L. Gerberding, director of the Centers for Disease Control and Prevention in Atlanta, said, this country ''could be locked out of the opportunity'' to develop vaccines and diagnostic tests. ''By taking steps to secure patent rights,'' she said, ''we assure that we will be able to continue to make the virus and the products from the virus available in the public domain.''

Mortality rates are bound to change somewhat as an epidemic continues. But unless the numbers fall drastically, SARS would be among infectious diseases with the highest death rates. Until now, fatality rates reported by the World Health Organization had ranged from 2 percent, when the epidemic was first detected in March, to 7.2 percent. The new SARS findings come from a statistical analysis of 1,425 patients suspected of having SARS who were admitted to Hong Kong hospitals from Feb. 20 to April 15. Overall, their mortality rate was estimated to be as high as 19.9 percent. On Tuesday, the WHO said the number of new SARS cases in Hong Kong had steadily declined, which officials said suggested that the outbreak there had reached a peak. So far, Hong Kong has reported 1,646 probable cases and 193 deaths, which would mean that the death rate was 11.7 percent

A look back shows striking differences in the way public health officials reacted to AIDS and SARS -- and it shows how much health agencies' quick response to SARS owes to the lessons of AIDS. The AIDS and SARS viruses damage the body in different ways. AIDS slowly attacks the immune system; symptoms take about 10 years to appear. SARS is faster: it takes 2 to 10 days, possibly as long as 13, from exposure to the onset of symptoms. Initially, each virus primarily affected young adults -- gay men for AIDS and health workers of both sexes for SARS. Because AIDS spreads through sexual activity, contaminated needles among drug injectors and from mothers to children, it still afflicts mostly young adults. But SARS spreads indiscriminately, and patients have varied more widely in age. But, for unknown reasons, SARS has largely spared children

The SARS virus is quite sensitive to changes in temperature, according to researchers at the National Institute of Infectious Diseases in Tokyo. At body temperature, the SARS virus survived less than four days, the Japanese researchers found. But it survived at least four days at refrigerator temperatures and seems to be able to survive forever at temperatures in a deep freezer. On plastic surfaces at room temperature, the virus could survive for two days, researchers said. The SARS virus is a new member of the coronavirus family, which includes viruses that can cause the common cold in humans and many more serious diseases in animals. SARS researchers have tried to extrapolate findings from known viruses in dealing with SARS. Scientists had known that infected individuals could excrete the SARS virus (at least in the RNA, or an immature form) for up to 30 days after onset of symptoms. But those findings reflected continuous production of the virus in the body. The new findings pertain to a significant difference -- stool outside the body

Hong Kong officials have found that 203 people with such contacts who were in quarantine developed SARS, [Klaus Stoehr] said. A large proportion of them had had contact with people who were infected at Amoy Gardens, an apartment complex where a large outbreak occurred. Hong Kong officials have theorized that the outbreak resulted from a sewage leak. The SARS virus is quite sensitive to changes in temperature, according to researchers at the National Institute of Infectious Diseases in Tokyo. At body temperature, the SARS virus survived less than four days, the Japanese researchers found. But it survived at least four days at refrigerator temperatures and seems to be able to survive indefinitely at temperatures in a deep freezer. On plastic surfaces at room temperature, the virus could survive for two days, researchers said. Meanwhile, less than a month after scientists cracked the genetic code of the SARS coronavirus, the virus is mutating, causing new forms of SARS to emerge in Southeast Asia

The WHO has said the SARS virus, which is a newly discovered member of the coronavirus family, is the cause of SARS. But the agency and other scientists agree that more work needs to be done to be certain. Scientists know that other coronaviruses have a high rate of mutation and so they say that it is far too soon to know whether the SARS virus will change to cause milder, or even more severe, illness, or become a seasonal disease, like influenza and other corona viruses. CDC researchers have developed a test like the Elisa, which is used to screen for the AIDS virus and other infectious agents. The SARS test is expected to have limited use because it cannot detect antibodies until three weeks after the onset of illness. A positive result would strongly indicate that an individual has been infected with the SARS virus, but a negative test will not necessarily rule out such infection, [Julie L. Gerberding] said

Laboratory tests found that detergents were far less effective in killing the SARS virus, [Klaus Stoehr] said. The SARS virus is quite sensitive to changes in temperature, according to researchers at the National Institute of Infectious Diseases in Tokyo. At body temperature, the SARS virus survived less than four days, the Japanese researchers found. But it survived at least four days at refrigerator temperatures and seems to be able to survive indefinitely at temperatures in a deep freezer. On plastic surfaces at room temperature, the virus could survive for two days, researchers said. The SARS virus is a new member of the coronavirus family, which includes viruses that can cause the common cold in humans and many more serious diseases in animals. SARS researchers have tried to extrapolate findings from known viruses in dealing with SARS. But many aspects of the new findings are surprising. For one thing, they show that the SARS virus is less stable at room temperature than other coronaviruses, particularly those that infect humans, Stoehr said

Mortality rates are bound to change somewhat as the epidemic continues. But unless the numbers fall drastically, SARS would be among the most lethal infectious diseases. Until now, SARS death rates reported by the World Health Organization had ranged from 2 percent, when the epidemic was first detected in March, to 7.2 percent. The new findings come from a statistical analysis of 1,425 patients suspected of having SARS who were admitted to Hong Kong hospitals between Feb. 20 and April 15. Overall, their mortality rate was estimated to be as high as 19.9 percent. By contrast, the influenza of the 1918 pandemic, which killed tens of millions of people worldwide, had an estimated mortality rate, overall, of 1 percent or less. The principal authors of the study, from the Imperial College in London, the University of Hong Kong, Chinese University of Hong Kong and Hong Kong health department, said their findings underscore that SARS is a serious threat to the public and that health officials and workers must act to contain it