Tracking a Killer Virus.

Dr. Clive Cockram remembers the last time he slept in the same bed as his wife. It was the morning of March 10, the day he and his colleagues at the Prince of Wales Hospital in Hong Kong found themselves at the forefront of one of the most troubling epidemics in a decade. At noon, his chief of staff announced that the hospital's own doctors and nurses had begun filling up the emergency wards--as patients. They reported trouble breathing, severe muscle pain and high fever. Their mystery illness wasn't responding to treatment. The healthy staff took to dressing from head to toe in protective gear. To avoid infecting his family, Cockram kept to a separate bedroom and wore a surgical mask at home. Many of his colleagues slept in their offices. In a few days, the wards filled up with more than 90 patients. "It was heartbreaking," he says. "This was a new disease, and we didn't know what to do. We felt so helpless."

The disease, dubbed SARS, for severe acute respiratory syndrome, has been the most vexing since the emergence of hantavirus a decade ago. Although SARS has a relatively low mortality rate--less than 4 percent- -it attacks the young and healthy as well as the old and frail. On Saturday, it claimed the life of 46-year-old Dr. Carlo Urbani, a disease expert with the World Health Organization who first identified the outbreak. SARS also spreads across borders with alarming speed. As of late last week, it had struck about 1,500 patients in 14 countries and killed at least 54. Even so, officials at the WHO were confident that tough measures taken only last week would contain the epidemic. Hong Kong and Singapore shut down schools and quarantined anyone who had come into close contact with patients. And health workers began distributing fliers at airports and training personnel to screen at- risk passengers. Hong Kong researchers hoped to make available a new diagnostic test. "I don't believe [SARS] will become a pandemic," says David Heymann, the Geneva-based head of communicable diseases for the WHO. "Overall, I think it's a positive picture."

That's not to say, of course, that more people won't get sick. But if the WHO is correct, the SARS investigation will go down as one of the swiftest and most successful ever undertaken. With ...