2003 April 03 Thursday
Why SARS Death Rate Lower In United States

There are 100 suspected cases of SARS (Severe Acute Respiratory Syndrome) in the United States with no deaths reported so far. By contrast, as of April 3, 2003 the World Health Organization has reported a cumulative total of 2270 SARS cases and 79 deaths.

Chinese authorities had previously reported a cumulative total of 1153 cases and 40 deaths in Guangdong Province from 16 November, when the outbreak began, to the end of March, making this province the area most seriously affected by SARS to date.

...

As of today, a cumulative total of 2270 SARS cases and 79 deaths have been reported from 16 countries. This represents an increase of 47 cases and 1 death (in Hong Kong) compared with yesterday.

Why the different death rates? Is the lower US death rate a reason to be complacent? Probably not. One reason is that US Centers for Disease Control and Prevention uses a different set of rules for identifying suspect SARS cases.

The majority of U.S. residents with SARS have recovered or stabilized clinically without specific antiviral therapy. The U.S. case-fatality proportion is lower than that reported in some other countries (3). Possible explanations for this include differing case definitions among countries or differences in the sensitivity of surveillance, leading to identification in the United States of patients with less severe or early manifestations of infection or of a larger proportion of patients with other respiratory illnesses. Until confirmatory laboratory testing is available, the case definition will include clinical criteria more likely to identify potentially infectious persons. Various therapies, including antiviral agents (e.g., oseltamivir or ribavirin) and corticosteroids, have been administered to SARS patients, but the efficacy of these therapies has not been determined.

Director of the CDC Dr. Julie Gerberding provides additional background on US CDC versus WHO SARS classification rules.

But with respect to your second question, why are the case patients in the United States having relatively mild illness, this is a conscious decision on our part to include anybody with fever and a respiratory symptom who had traveled to an affected area. The cases that WHO is including from countries on its list--at least most of the cases that are formally appearing on the WHO list--are only people who have the severe form of SARS, with the pneumonia. And so we are casting a broader net in this country because we want to be vigilant about identifying anyone who could possibly be infectious, and isolating them if they're sick, and advising their contacts how they can protect themselves. So not surprisingly, we do not have as many patients with pneumonia. In fact, I think we have altogether--I'll have to get back to you on the exact number, but less than 50 percent of our case patients have had pneumonia. And one of our case patients has required ventilation. But most of that is the artifact of the way in which we are conducting our evaluation and our epidemiologic assessment. Actually, about 20 of the case patients have been diagnosed with pneumonia.

Once an accurate test for SARS infection becomes available (and it looks like scientists are fairly certain that a coronavirus is the cause) then methods of classifying SARS victims can become more uniform. Dr. James Hughes of the CDC reports on progress in the development of SARS tests:

DR. JAMES HUGHES: In terms of the serologic testing, realize that 10 days ago we didn't have any antibody test to detect evidence of infection with this previously unrecognized corona virus. As a result of a lot of hard work that's been done here over the past 10 days, we now have two that look promising. One is an indirect fluorescent antibody test, and the other is an Eliza. More work needs to be done to validate these tests. I would remind you that these are tests that are not approved for routine use for patient diagnosis yet--not surprisingly, since they've just been developed. So we have to interpret results using these tests with caution. Having said that, they look promising in that they appear to perform well in suspect cases, particularly a subset of those that are relatively more severe. We have looked for evidence of this antibody in roughly 400 sera collected recently from people in this country without any suggestive evidence of SARS, and they're negative in all of those people.

If the indirect antibody test measures immune response to the virus (not sure, does anyone know?) it could be very useful for identifying recovered victims who no longer have the SARS virus in their bodies. This would be incredibly helpful because people whose immune systems have fought off the SARS virus could be used as blood donors to extract gamma globulin immune system molecules from their blood. The gamma globulin can be used to treat the most severe cases of SARS.

Whether SARS is eventually controlled continues to strike me as being heavily dependent on whether it reaches less developed places where the public health infrastructure is nearly non-existent. Let it get loose in India and it seems like it would become impossible to control.

By Randall Parker at 2003 April 03 02:25 PM 
Comments

the brown flipside-at least the indian government would probably be far more transparent and willing to cooperate with WHO authorities.

Posted by: razib on April 3, 2003 11:07 PM
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