New Bug No Surprise

May 26, 2003

Heather Heilman

No one yet knows just how severe is the acute respira tory syndrome (SARS) that emerged last fall in China's Guangdong Province. But we shouldn't be surprised at the appearance of a new disease, according to Susan McLellan, associate professor of medicine in the section of infectious diseases. "We should expect things like this, because there are millions of bacteria out there that we haven't identified yet," she said.

At this writing, scientists in the Netherlands have just confirmed that a new form of coronavirus is the cause of SARS. Humans have long been hosts to coronaviruses, which cause cold symptoms. The evidence right now seems to suggest that it emerged from an animal virus, one that randomly mutated into a form that could be transmitted to humans.

"Alternatively, you could have a situation where you could have human and animal populations in high density, and by random luck a human might get an animal virus into their system," McLellan said. "It might not make them sick by itself, but if it exchanges some genetic material with a human coronavirus, you could end up with a new virus that transmits among humans as easily as a cold, but causes a more severe disease."

A test for the virus should soon be available, and drugs to combat it may not be far behind. Except for the Chinese government's initial reluctance to admit the problem and share information, McLellan believes the outbreak has been handled well.

"I think the response has been really quite phenomenal," she said. "There was the extremely rapid identification of the agent, fairly good success with isolation measures, and the quick development of a test to prove if a person has it or not."

It helps that the disease seems to be transmitted most by people who are symptomatic--unlike diseases like polio that can be spread by carriers with no symptoms. But that doesn't mean the problem is solved.

"It's still very much a touch-and-go situation," McLellan said. Controlling the disease depends on being able to isolate those who have the disease, which requires their cooperation. But even in Hong Kong, there have been a few instances of people resisting quarantine. McLellan worries about what might happen if the disease spreads to places like Sub-Saharan Africa, where people often fear the health-care system.

"When you have a situation where the population is afraid to admit that they might have it, then they're going to continue to transmit it," she said. The United States has so far been spared a serious problem with SARS, with only a few cases traceable to carriers who got off a plane from Asia or Toronto. "Most of the people on international flights are educated enough to read the information and behave appropriately," McLellan said. "That's why there's been very little transmission in this country."

But should the pattern change and the virus make its way into, say, an inner-city population where people are afraid to come in for health care, it could become a more serious epidemic in the United States. The rate of fatality with SARS is fairly low, around 3 or 4 percent. Most of the people who've died from the disease have been elderly or were in poor health even before being exposed to the virus. (At this writing there's some evidence that a more virulent strain might be emerging in Hong Kong.) But 10 percent of people who are infected will need ventilatory assistance, and many may spend several weeks in the hospital.

"Even in a country with decent health care, the services can easily become overwhelmed by the number of people who end up needing a lot of support," McLellan said. Still, being aware of potential dangers is one thing and panicking is another. "I think we need to be a bit careful not to overreact," she said.

Heather Heilman can be reached at

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