SARS, the mysterious respiratory illness that is crisscrossing the globe, has claimed at least nine more victims since Saturday. The disease's overall mortality rate, approximately 4 percent, is roughly equal to that of measles, but the uncertainty surrounding its cause and how it spreads continues to make it a serious public health issue. In addition, the threat of SARS continues to disrupt international business and tourism.

As of Monday afternoon, the disease had claimed 98 lives and infected more than 2,600 hundred people around the globe, according to the World Health Organization (WHO). The Centers for Disease Control and Prevention (CDC) is investigating 115 suspected cases of SARS in the U.S.; and in Toronto, the North American city most affected by SARS, 10 people have died. All of the victims had traveled to Asia or had direct contact with a SARS-infected patient in a home or hospital setting, according to Paul Gully, senior director general of the population and public health branch of Health Canada.

The relative ease of international travel has been critical in allowing SARS to affect regions around the globe. Indeed, WHO has advised travelers to postpone nonessential trips to Hong Kong Special Administration Region and China's Guangdong Province, where the disease originated in November. In part because of decreased demand for the route, Continental Airlines announced on Monday that it would suspend nonstop service from Newark Airport to Hong Kong as of Thursday until the end of May. The WHO has also suggested screening all international travelers leaving any of the seven affected areas in Canada, Vietnam, China and Singapore. Travelers leaving Toronto's Pearson Airport, for instance, are now greeted with pink Health Alert Notices that outline the symptoms of the disease and advise travelers to postpone their trips if they meet one of the following criteria: they are experiencing SARS symptoms, which include high fever, chills, sore throat, cough or difficulty breathing; they have had contact with a SARS-infected person in the past 10 days; or they have visited a public health facility that has been affected by SARS.Ticket agents will also question passengers more thoroughly regarding their understanding of SARS later this week, according to Health Canada officials. In addition, passengers on flights to and from Beijing, Hong Kong and Singapore will be asked en route to fill out questionnaires and provide contact information for the two weeks following their arrival.

The WHO now has 11 laboratories in nine countries working to find the causative agent behind SARS and to develop a reliable diagnostic test. A previously unknown type of coronavirus is the leading candidate for the cause of SARS, according to the CDC. The novel virus is present in 60 percent of Canada's cases of SARS, says Frank Plumber, the science director general of Health Canada's National Microbiology Lab in Winnipeg. "There is a link," he says, "but it's not as solid as I would like to see it." Because 40 percent of the country's SARS patients did not test positive for the pathogen, Plumber suspects that the new coronavirus is not the only cause of the disease. "It's definitely a new virus and it's definitely circulating," he comments, but the question remains whether something else could be responsible for the illness.

Currently no treatment for SARS itself exists, but doctors can treat the symptoms. People potentially exposed to the virus are asked to quarantine themselves for 10 days to reduce the spread of the disease. So far, thousands of people in the greater Toronto area have been quarantined. Last Friday, President Bush signed an executive order that added SARS to the list of diseases for which public health officials can forcibly quarantine Americans if they do not agree to do so on their own. It was the first such addition in two decades.