In the U.S., CBS News Correspondent Elizabeth Kaledin reports, the Centers for Disease Control is advising Americans to postpone any non-essential travel to mainland China, Hong Kong, Singapore and Hanoi.
Canada is the other trouble spot. A fourth death and an infected child have led health officials in Toronto to restrict visitors to all hospitals in the province.
"What happened in Canada is that the early cases arrived before this disease was recognized," said CDC Director Julie Louise Gerberding. "So there was an opportunity for the chain of transmission to get established there. So in a sense, the cat is out of the bag in Canada."
American health officials see no reason to curtail travel to and from Canada, saying the Canadian and American SARS outbreaks are very different. Still, there's plenty of anxiety about the spread of this potentially fatal pneumonia-like illness. Experts warn it is easily transmitted through coughing or sneezing, leading to concern about the safety of public spaces.
"This virus is spreading much like the common cold virus, and that's worrisome because it is efficiently spread, at least in people who have close face-to-face contact," noted Gerberding.
Even die-hard Toronto Blue Jays fans were reluctant to attend the home opener against the New York Yankees, fearing the Skydome would be like one big Petri dish.
In the lab, progress is being made in identifying the cause of SARS. Some say we could know in days.
Scientists are also close to developing a diagnostic test. Still, Kaledin reports, breakthroughs can't come rapidly enough to stop this rapid-fire health threat.