Peril From The East

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Paradoxically, the existence of superspreaders could be good news: if just a few victims are responsible for the bulk of the outbreak, the disease should be easier to control with aggressive quarantine measures. Some doctors have also postulated that as the virus radiates from the initial patient, it becomes less virulent, meaning that those who come down with second- or third-generation infections may be in less danger. That could explain why in Europe nobody has died and most cases have not turned out to be life threatening. Says Dr. Joseph Sung, chief of clinical medicine at Prince of Wales Hospital: "I'm quite convinced that some people might have contracted the infection but not the disease. Some may develop mild symptoms, like a little bit of cough and no fever; some may just feel a little tired for a day or two."

Mild cases would also act like natural vaccines, conferring immunity on the patients. When 70% or so of a population has immunity — what epidemiologists call herd immunity — a virus is considered burned out: it can't spread further because there is almost no one left to infect. In the meantime, hospitals are trying to prevent the disease from taking root by isolating patients and using gowns, masks, goggles and gloves religiously — techniques that so far have proved extremely effective at preventing transmission.

Still, while the number of new cases in such hot spots as Singapore, Hong Kong and Vietnam finally began to drop last week, nobody is prepared to say that this outbreak is even close to being over, especially considering that many residents of Hong Kong's Amoy Gardens apartments fled before officials could arrive to take them into quarantine. "I don't want to give anybody a false expectation that this is under control," says Ostroff. "This is still a very fluid situation."

So while public-health officials stay on high alert for any new cases, researchers are trying to erase any lingering uncertainty about the ultimate cause of SARS. Several kinds of diagnostic test are nearly ready. A vaccine against the coronavirus is already under development. And epidemiologists in Asia, Europe and North America are piecing together the natural history of SARS. That last effort should be made a lot easier with the Chinese government's decision last week to finally let a who team into Guangdong. Medical detectives may have already found the very first recorded victim — patient zero — a man in the city of Foshan who passed the virus on to four other people before he recovered.

Even if all these measures fail to eliminate SARS quickly or completely, they should at least minimize the danger. "People should be concerned," says Ostroff. "But I don't think they should be alarmed." The minuscule murderer in Dr. Nicholls' microscope sights is still potentially deadly. But it no longer looks like the monster it appeared to be just a few weeks ago.