Experts say eventual spread of mystery disease is likely

Can severe acute respiratory syndrome be stopped? As hard as public health officials work to stamp out the virus, many experts reluctantly conclude it is likely if not inevitable that it eventually will spread everywhere.

The highly contagious disease has already sickened more than 2,000 people, and new cases appear daily in Hong Kong, despite an all-out effort to isolate victims and quarantine those at risk.

Experts acknowledge that the eventual course of any new disease is almost impossible to predict. Some frightening new infections have burned themselves out, while others, like AIDS, have become global disasters.

However, several features of SARS make epidemiologists, virologists and infectious disease experts fear total victory is unlikely.

"Will it explode into a major epidemic that will propagate over the years? Or will it fizzle out or be contained at a low rate? That's unknown," said Dr. Lee Harrison of the University of Pittsburgh. "I suspect we will see this disease for at least the next several years. It's hard to imagine it will be over soon."

Trying to minimize spread

Perhaps the most ominous sign is the steep climb in new cases, especially in Hong Kong, which has had a nearly fourfold increase in just two weeks. Each person who gets it may spread the infection to several others before they even know they have it.

While many are infected through face-to-face contact, evidence is mounting that the virus may also spread through the air or be picked up from contaminated surfaces.

Besides quarantining the sick, health officials have tried to minimize SARS' spread by urging people with suspicious symptoms not to fly on airlines.

However, some experts worry that those who are clearly sick may not be the biggest concern.

People catch bad colds from friends who have mild ones. And the same may be true for SARS. Those who have slight symptoms or even seem well could still spread the disease. In such a scenario, isolating the sick and quarantining their contacts will not work.

"We may be able to slow transmission, but we won't be able to stop it if there are many other cases of milder disease out there," said Dr. Arnold Monto, a University of Michigan epidemiologist.

Although the cause of the outbreak has not been proven beyond doubt, investigators say most evidence points to a previously unknown version of the coronavirus, the bug that causes about a third of all colds. Some who study this family of viruses say that because it spreads through coughs and sneezes, they cannot imagine totally wiping it out now that it has infected so many people.

Some suggest that even if this outbreak dies down, the virus could pop up again with no warning or it might follow a seasonal pattern, like colds and flu.

Just how it acts in the long run will depend on its genetic makeup and origins. Birds and other animals have their own versions of coronavirus, and some of them cause much worse disease than the human type. Researchers say SARS may be caused by a coronavirus that moved from animals to people. Or perhaps it is a standard human coronavirus that picked up menacing genes from an animal version of the virus.

Such leaps have happened in the recent past. The hendra virus spread from horses to people in Australia, while the nipah virus went from pigs to humans in Malaysia. However, neither bug then spread from person to person.

But SARS has found a home in humans. Experts say it could grow less virulent as it reproduces inside the human body and then passes on, or it might grow worse.

Whatever happens, the virus is likely to change over time, says Dr. Michael Lai of the University of Southern California, a coronavirus expert. This variety of viruses mutates and swaps genes frequently.

"The severe problems we are seeing right now might represent a very small minority of the coronavirus infections," Lai said.

The World Health Organization is still officially optimistic. "We think it's possible that this disease can be beaten back, that with more effort this doesn't have to get out of hand," said Dick Thompson, a WHO spokesman.

Such an outcome is far from definite, cautioned Dr. James Hughes, infectious disease chief at the U.S. Centers for Disease Control and Prevention. He called SARS "an urgent global public health threat" and added: "I think we had better all keep an open mind here. We've seen it spread very dramatically and very rapidly."

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EDITOR'S NOTE: Medical Editor Daniel Q. Haney is a special correspondent for The Associated Press.

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On the Net:

CDC: http://www.cdc.gov/ncidod/sars/news.htm

WHO: http://www.who.int/csr/sars/en/