It seemed , in the early months of 2003, that the disease came out of nowhere. No one could pinpoint the first case of severe acute respiratory syndrome (SARS)—it probably occurred in November 2002—but by early 2003 it was roaring through hospitals in China and other parts of Asia, as well as in Toronto, Canada, striking down hundreds of doctors and nurses as they tried to care for their patients. It was a ghastly illness; one Hong Kong resident says that watching someone with SARS gasp and fight for breath was "like watching a man drown to death on dry land."Thousands of those infected died, and doctors were panicking, for there seemed to be little progress in fighting the new disease, and it continued to spread. As people quickly learned, a dangerous new disease in the age of jet travel rapidly...