Geodog

Doing the SARS numbers

In a discussion on Dave Farber's IP list, someone asked:

>1.    If a virus is aerosol and has an 

>incubation period of 7+ days, is it

>possible to contain it geographically 

>without ceasing all air travel?

It isn't clear from my reading whether people infected with SARS can transmit it before they have symptoms; it sounds like the CDC doesn't know either. From the updated CDC FAQ posted today:

How long is a person with SARS infectious to others?
Information to date suggests that people are most likely to be infectious when they have symptoms, such as fever or cough. However, it is not known how long before or after their symptoms begin that patients with SARS might be able to transmit the disease to others. (CDC SARS FAQ)

If infected people can transmit the disease before they feel ill, then until we have a reliable test for the virus that causes SARS, it seems the only way to stop the spread of SARS is to cease all air travel to and from areas where it is endemic, or to quarantine travelers for 7-10 days. This is how epidemics were stopped before the modern age of medicine, and until there is a vaccine/treatment, this will be the only way to stop SARS. Of course, the economic costs of stopping travel will be enormous - no one wants to face that. However, they don't get any cheaper by waiting. I can't believe that there are still flights from Hong Kong landing in the US every day. But it's true. The longer we wait before instituting quarantines, the greater the number of people who are going to die, and the greater the economic costs.

> 2. At last check, there were approximately 50 deaths of 2500

>reported cases. Given that the number of actual "exposures"

>is likely significantly higher and that many individuals who

>contracted the virus were able to defeat it without major

>symptoms and therefore did not report; Are viruses with a

>mortality rate of less than 2% (potentially MUCH less)

>considered a global crisis? Is there possibly some other

>reason for the significant media coverage?

Given than SARS is a diagnosis of exclusion, and the definition is currently very wide, I suspect that it is equally likely that a lot of people are labeled as having SARS who don't, so the true mortality rate could be considerably higher than the 4% they are currently guessing. Until we have a reliable test for the virus, we won't know what the true mortality rate is. Even so, if this became as prevalent as the flu, which around 15% of the US population gets every year (http://www.cdc.gov/ncidod/diseases/flu/fluinfo.htm), a mortality rate of 2% gives you *870,000 deaths* in the US a year. That's pretty big. And if the mortality rate is 4%, the US would lose one and half million people. Makes Osama bin Laden look like a piker.

The other part is that for every person who has died of SARS, there are at least 10 people still in hospital intensive care units breathing only with respirators (In 10%--20% of cases, the respiratory illness is severe enough to require intubation and mechanical ventilation http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5212a5.htm). Using the math above, that gives you ***6 and a half million people in ICU's on ventilators***, which isn't going to happen. That is both horrifying from a human perspective, and alarming for the kind of stress it would put on our already stressed medical system. We don't have 1/10th that many ventilators. The mortality rate will go up a lot if SARS gets that widespread.

I think that there is enough in the disease itself, and in likely hypothetical scenarios, to explain all the media attention. I just wish there was more media attention, and more demands for preparation and action.

Cross posted at SARS Watch Org