Is SARS Getting Deadlier?

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SARS epidemic may be waning in some of its hot zones in the world, but scientists aren't ready to put away their petri dishes and declare victory yet. They know, through long experience trying to eradicate AIDS and other persistent diseases, that pathogens like the mutated coronavirus believed to cause SARS are full of surprises—and that most are nasty ones.

Just last week, for example, the World Health Organization (WHO) announced the disturbing disclosure that SARS may be far deadlier than previously believed. A growing body of statistical evidence now indicates that about one out of every 10 people who contract the disease is killed by it. That's twice the fatality rate doctors had initially predicted.

Equally worrisome, the virus is also proving to be more tenacious than the medical community had hoped. In Hong Kong, doctors reported that, for unclear reasons, 12 recovered SARS patients had relapsed weeks after they had been discharged—spurring fears that people may be infectious even after they've left isolation, which could spark new outbreaks in areas where SARS has been brought under control. That possibility becomes more ominous if, as some doctors suggest, there are some people who come down with SARS without showing symptoms—meaning they could unknowingly spread the disease far and wide even under the strictest quarantine regimes. All of this underscores how much remains unknown about the virus, identified for the first time in late March. Says Dr. Klaus Stohr, scientific director of the WHO's SARS investigation: "We're sailing a boat while we are still building it."

Most alarming, though, is the rising fatality rate. During SARS' international onset some two months ago, when doctors had only a handful of cases to examine, the mortality rate was thought to be about 5%—scary, but not exactly on the scale of Ebola. What's more, those most at risk were typically the elderly and the chronically ill. But as the cases have piled up, so have the fatalities, including healthier individuals in their late 20s or early 30s. In Vietnam the death rate is around 8%, Singapore at nearly 12% and Toronto 13.5%. In Hong Kong, where baffled health officials held onto the 5% figure like a life preserver for weeks, the mortality rate has now passed 10%, with a cumulative total of 179 fatalities by the end of last week. "This is very worrying," says Professor John Tam, a microbiologist at the Chinese University of Hong Kong.

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The fluctuating toll may be partly due to regional statistical idiosyncrasies. In Hong Kong, for example, many of the recent fatalities were residents of Amoy Gardens, an apartment complex where at the end of March more than 200 people contracted SARS in a matter of days—producing a logjam of critically ill patients who are now beginning to die, as it takes several weeks for SARS to claim its victims. More unsettling are reports from several laboratories that the coronavirus responsible is mutating almost continuously as it spreads, raising the possibility that certain strains may be more vicious than others.

Compounding the problem, doctors still haven't come up with a verifiably effective treatment anywhere. In Hong Kong, clinicians are continuing to use the antiviral drug ribavirin, though tests in the U.S. have shown that it doesn't kill the coronavirus. Several kinds of vaccines are already in the works, but private companies are hesitant to spend money on a virus that could disappear soon. That means most of the research is left to the cash-strapped public sector, and progress is slow. Even the most optimistic researchers believe a vaccine will take two years to develop—assuming the virus doesn't shape-shift as readily as HIV, making it almost impossible to produce a one-size-fits-all vaccine.

Some scientists are not even sure the coronavirus is the sole agent behind SARS. According to Dr. Frank Plummer, director of Canada's National Microbiology Laboratory, the SARS coronavirus is showing up in only 40% of Canada's probable cases. Though the WHO is holding fast to the belief that SARS is caused by a mutated coronavirus, Plummer says, "In our data, the association between the coronavirus and SARS seems to be weakening rather than strengthening."

Fortunately, at the moment there's little evidence to suggest the disease has shifted gears and spreading more rapidly than before. In fact, absent the kind of environmental factors that facilitate large-scale outbreaks like Amoy Gardens' where one superspreader is believed to have discharged a large viral load into the complex's dodgy plumbing system, SARS doesn't seem to be as contagious as first feared. On average, say epidemiologists, each sufferer infects only two people, compared with 16 victims for a person with measles.

When scientists sequenced the SARS coronavirus genome three weeks ago in record time, the coup was hailed as a milestone in medical history. And it was indeed a remarkable sign of how far medical research has come. But discovery often leads to greater uncertainty. "There aren't a lot of infectious diseases like this," says Dr. Ian Lipkin, a virologist at Columbia University. "This is a new virus we haven't encountered before, and we still don't understand a lot about its behavior." Scientists will eventually unravel much of this mystery. They just need more time. Here's hoping they can move as fast as the disease itself.