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Volume CXXXII, Number 21 |
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Surviving SARS
JEFF BENSON, M.D.
Dear Dr. Jeff: If a mutant cold virus causes SARS, does that mean it's possible for a cold to turn into SARS? C.B.
Dear C.B.: For most viruses, frequent genetic mutation is in fact the rule, rather than the exception. The vast majority of these transformations render viruses less infectious. Other mutations change proteins on the outer coats of the viruses, giving them a new immunologic identity and allowing them to slip undetected past our immune defences. That's why we keep getting "common colds," usually caused by continually changing coronaviruses. The SARS coronavirus mutation, however, gave it a new protein coat and made it far more dangerous.
Although more details become clearer every day about SARS, the overall picture remains complex and confusing.
As of April 15, according to the World Health Organization, there have been about 3,200 reported cases of probable or confirmed SARS worldwide. 1,418 have been in China, 1,232 in Hong Kong, 162 in Singapore, and 63 in Vietnam. Canada has had 100 cases (almost exclusively in Toronto), and the U.S. 193.
The illness seems to act differently in different countries. The case fatality rate, for instance, varies greatly.
In the U.S., there have been no deaths from SARS. In China and Hong Kong, however, the case fatality rate has been about 4.5 percent. In Canada, it is now 13 percent. These differences may in part reflect statistical variance from the relatively small numbers involved or may raise the possibility that there are different co-factors involved.
The illness clearly affects different people very differently. Authorities now describe "super-spreaders" as people with SARS who seem to infect many others around them, whether they are family members, ambulance drivers, or patients in the same emergency room. In the U.S., SARS cases have not "clustered" as much as they have in Hong Kong and Toronto, and those affected by SARS have largely had relatively mild illnesses. In fact, one public health official recently suggested that American SARS ("Severe Acute Respiratory Syndrome") be renamed MARS ("Mild Acute Respiratory Syndrome"). Suspected SARS cases in the U.S. are spread across 32 states, although New York and California together account for one-third. It remains unknown whether or not people without symptoms can harbor and spread the SARS virus (which would make them so-called "silent spreaders").
Scientists in Canada and the U.S. have now identified the entire 29,727-nucleotide sequence of the SARS coronavirus genome. Significantly, although the specimens were derived from different patients who had been infected in different countries, the viral genetic codes were virtually identical.
This suggests that the SARS epidemic did in fact emerge from a common source. Moreover, the whole genome is new, according to Hong Kong researchers and derived not from human but from animal viral sources.
Some of SARS' epidemiologic differences may also reflect diagnostic difficulties. The diagnosis of SARS remains clinical and what doctors call a "diagnosis of exclusion." The C.D.C. (Centers for Disease Control and Prevention) case definition of SARS specifies that the illness have no other known cause; that it include measured fever greater than 100.4 degrees, significant cough, and shortness of breath; and that it begin within 10 days of travel to an affected area, or within 10 days of close contact with a person who has a respiratory illness, who traveled to a SARS area or who is known to be a suspect SARS case.
Laboratory tests can confirm the diagnosis of SARS but only after considerable delay. Antibody tests, for instance, take up to 3 weeks to complete. Hopefully now that the SARS coronavirus has been definitively confirmed as the primary cause of the illness and its genome fully identified, faster and more accurate clinical lab tests will be developed.
At this point in the epidemic, the C.D.C and W.H.O. make the following recommendations to Americans regarding prevention and travel. Noting that to date, all reported cases of SARS in the U.S. have occurred after travel to affected areas or through close contact with SARS patients, both agencies recommend postponing non-essential travel to affected areas and using appropriate protective equipment and techniques (basically masks, gowns and gloves) around those suspected to have fallen ill with SARS.
In general, all of us should take care to practice basic hygiene, like regular hand washing and avoiding contact with others' respiratory droplets. Travel advisories are currently limited to China, Hong Kong, Singapore, and Vietnam. There are no travel advisories for Toronto.
One last point to consider: it is always very frightening when a new pathogen, a new illness and a new epidemic break out. Keep in mind, though, that at least so far, SARS pales in comparison to far better known and far more common public health threats. Influenza, which early or mild SARS mimics, but which, unlike SARS is a vaccine-preventable disease, infects 10 to 20 percent of the entire population every year, killing some 36,000 Americans annually.
Drunk drivers kill over 17,000 Americans every year or nearly one person every 30 minutes. A full 30 percent of all cancer deaths are caused by smoking, and over one-third of people who smoke will die prematurely from their use of tobacco. And more than 2,600 Americans die every day of cardiovascular disease. That averages out to 1 death every 33 seconds. The majority of those deaths are also premature and preventable.
A great deal of information is available about SARS. The Maine Bureau of Health (www.state.me.us/dhs/boh/ddc/indexnew.htm), C.D.C. (www.cdc.gov/ncidod/sars/), and W.H.O. (www.who.int/csr/sars/en/) all have web-posted information that is frequently updated. National Public Radio continues to air thoughtful and well-informed discussions about SARS. You can find audio archives or order transcripts on-line at www.npr.org.
So: read up, stay calm, and wash your hands!
Jeff Benson, M.D.
Dudley Coe Health Center
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