SARS Lessons Unlearned
Will SARS hit hard again this year or in the future? Experts go over what happened and what may be next.
What ended the SARS epidemic? Klaus StÃ¶hr, PhD, director of the
WHO's global SARS laboratory network, credits early identification and
isolation of SARS patients. It took heroic efforts from health officials in
Hong Kong and elsewhere, who refused to allow anyone with a fever to board any
form of transportation. Moreover, air travel to cities with ongoing SARS
outbreaks virtually ceased.
"Most countries did temperature screening," StÃ¶hr tells
WebMD. "In Hong Kong, every day there were 750,000 people screened at
airports, seaports, and land ports. Every day, several hundred people were
found to be feverish, and quite a number turned out to be suspected cases of
SARS. That is one measure that worked to limit the number of cases. Also
helpful was the recommendation to the public to suspend air travel to countries
where SARS cases were occurring in the community. These are two measures that
we considered successful."
As it turned out, SARS wasn't as easily spread as it first
seemed. Most cases could be traced to "superspreaders" -- a few people
who became especially ill with especially large doses of especially infectious
"People who were relatively close to the original source of
infection obtained a larger dose of SARS virus, were more severely ill, and
secreted a large amount of virus," StÃ¶hr says. "With each link in the
chain of transmission, the virus excretion rate changed. Those first in the
chain were most severely infected. But the super spreading was mostly seen in
the initial phase of the outbreak when people did not understand the measures
that needed to be taken."
Where Did SARS Come From -- and Where Is It Now?
Foshan, China, is in Guangdong province. As elsewhere in
southern China, Guangdong markets feature exotic "game food." These
live, exotic animals of nearly every imaginable kind are caged very close to
one another. They're butchered and eaten as culinary delicacies.
Some of the earliest SARS cases seem to have been in people
whose jobs involved dealing with these animals. Blood from people who handle
these animals are more likely to have antibodies against the SARS virus than
other people working in the same markets. And health authorities have isolated
SARS virus from at least two kinds of these animals -- the Himalayan palm civet
and the raccoon dog.
This doesn't necessarily mean the animals are the source of
SARS. It's possible that the animals caught the virus from humans, and not the
other way around. Pets owned by SARS patients in Hong Kong -- cats and dogs --
have been infected with the virus.
StÃ¶hr says it's clear that no humans now have SARS disease.
This means there are only five ways the disease could make a comeback:
The SARS virus is hiding in humans. These people would be infected but
without symptoms. StÃ¶hr finds this unlikely. Intense, ongoing screening of
blood donors and health-care workers in Hong Kong finds no trace of active SARS
infection. This fits with the idea that SARS can only be spread by people who
are severely ill. "Asymptomatic carriage, if it happens, plays a small
role," StÃ¶hr says.
- Silent transmission. If some people got infected but never had an immune
response to the SARS virus, they couldn't be detected by SARS screening tests.
"This has not been seen at all," StÃ¶hr says.
- The virus might get away from a laboratory where it's being studied. Labs
studying the virus might store it unsafely. This happened twice. In the first
incident, a lab worker in Singapore became infected. He did not spread the SARS
virus, even though he came into close contact with 25 other people. More
recently, a worker in a Taiwan military lab was accidentally infected in
December 2003. This case is more troubling, as the worker traveled to Singapore
after becoming infected. A WHO investigation -- including tracing of all
contacts -- is under way.
- A more sinister possibility is the intentional release of the virus.
"We do have to be concerned about this virus as it sits in refrigerators
around the world," Low says. "I am worried about SARS as a bioterror
weapon. It's already been shown to be very effective in bringing health care to
- If SARS came from animals the first time, it could happen again. "If
the original animal reservoir is not detected, one cannot rule out
re-emergence, especially as in China there has been no attempt to segregate
exotic animals in the marketplace," StÃ¶hr says. "These animals have
been allowed back into the markets and are still a threat." But Low sees
this as a sign that the original emergence of SARS from animals was a one-time
event. "There is no evidence it ever happened before and -- even though the
same circumstances remain in place -- it hasn't happened since," he