- The death toll from SARS rose again yesterday, bringing
to 15 the number of people who have died from the disease in Canada. Ontario
Health Minister Tony Clement, far left, said at a news conference in Toronto
yesterday that up to 100 more people will be reassigned to Toronto public
health units to relieve exhausted staff.
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- Canada's top virus hunter, Francis Plummer, a veteran
scientist who has spent 20 years tracking AIDS and other deadly infections
around the globe, said he is not convinced by the theory that SARS is caused
by a rogue strain of coronavirus.
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- Dr. Plummer said tests show only 40% of Canadian SARS
patients have the suspect virus in their tissue samples and even these
patients have small amounts of it. Moreover, some people who test positive
for coronavirus have no SARS symptoms.
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- "The link between SARS and the virus is quite weak,"
said Dr. Plummer, scientific director of the National Microbiology Laboratory
in Winnipeg.
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- Although labs in Hong Kong and the United States have
found similar results, scientists there have not been as vocally skeptical
of coronavirus, identified shortly after SARS turned up in Hong Kong and
Canada. But researchers agree no test can definitively rule in or exclude
SARS at this time.
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- Dr. Julie Gerberding, head of the U.S. Centers for Disease
Control and a proponent of the coronavirus theory, said there may be good
reasons for the discrepancy between the number of cases and the number
of patients who test positive for coronavirus.
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- "First and foremost is probably because [patients]
don't have SARS and they don't have coronavirus infection," she told
a briefing yesterday. "They have some other respiratory illness that's
caused by something else. Another explanation is that although we have
tests that can identify it when it's present, we don't know how sensitive
they are."
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- Making things more difficult, said Dr. Gerberding, is
that if a specimen is not taken early enough in the disease's progression,
the test might not detect the presence of a virus.
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- "Even with influenza, which is an illness that we
have very good tests for, if we don't do certain tests early in the course
of influenza, the tests are negative -- they're simply done too late,"
said Dr. Gerberding.
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- Scientists now use two methods to search for a cause
of SARS.
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- In the first, they take nasopharyngeal fluid -- nasal
swabs -- within 72 hours of symptoms and test the samples directly for
the presence of coronavirus using a tool called PCR. This tool is so sensitive
it can detect the genetic material of a single virus and amplify it many
times. So far, about 40% of Canadian SARS patients have tested positive.
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- In the second method, doctors take blood samples from
SARS patients and test the serum for antibodies.
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- Ordinarily, the body produces these tiny proteins when
exposed to foreign invaders, like a coronavirus. The process takes six
days to three weeks. Yet only about one-third of SARS patients in Canada
test positive for antibodies to coronavirus, said Dr. Plummer.
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- "To me, that is very, very odd."
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- Dr. Plummer notes all the Canadian cases of SARS have
been linked by direct exposure to infected patients, so one would assume
that all cases would test positive for the same virus. Yet they don't.
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- And while some SARS carriers seem to be extremely infectious,
earning the nickname "super spreaders," others spread it less
readily. For example, a single patient who travelled from Hong Kong spread
the disease to dozens of others in Canada. Yet among the 39 cases of SARS
in the United States, 37 were travellers who were probably infected abroad,
while only two people were infected in the United States.
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- Although coronavirus is still a leading candidate, many
scientists believe SARS may be linked to human paramyxovirus, identified
by Dr. Plummer's lab several weeks ago as a potential cause. However, other
researchers think the virus is simply an "innocent bystander"
that just happens to be present in many people, including SARS patients.
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- >http://www.nationalpost.com/national/story.html?id=
- 676B30D0-7F34-423A-A896-64F82D3C6C89
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