X-Message-Number: 21555
Date: Sun, 06 Apr 2003 15:28:56 -0400
From: Keith Henson <>
Subject: Re: SARS update, April 5, 2003 [Charles Platt]

At 09:00 AM 06/04/03 +0000, Charles Platt wrote:

>Message #21547
>Date: Sun, 6 Apr 2003 03:24:21 -0400 (EDT)
>From: Charles Platt <>
>Subject: SARS update, April 5, 2003
>We now have three weeks of SARS data from the World Health Organization;
>i.e. 18 data points (the bureaucrats at W.H.O. seem to feel no pressing
>need--yet--to report data on Sundays). The obvious question is: Do the
>data points constitute a trend?
>An acquaintance of mine who shall remain nameless (mainly because I
>wouldn't want to embarrass him) has spent a surprising amount of time
>plotting curves on log paper in an attempt to measure the "doubling time"
>of cases in nations where the virus is active. As I recall from my distant
>educational past, if you have an exponential growth rate, the data should
>appear as a smooth upward-trending curve on normal graph paper but will be
>displayed as a straight line on log graph paper; and if you measure the
>slope of the line, you can derive the doubling time.

Posted with permission from another list:

Date: 4 Apr 2003 12:55:18 -0800
From: Ted Kaehler <>
Subject: Graph of SARS cases in US and Worldwide
<!doctype html public "-//W3C//DTD W3 HTML//EN">

I am quite alarmed by the spread of the new disease, SARS. It is rising 
exponentially, in spite of a concerted effort to contain it by health 
officials in Asia.

I have prepared a web page with a graph on log paper, and have computed the 
doubling times. http://squeak.org/us/ted/sars-graph.html Feel free to tell 
others about this page. The graph will be updated every day as new 
statistics come out.
As of April 4th, world cases are doubling every 10 days. World deaths are 
doubling every 11 days, and cases in the US are doubling 7.7 days. Most of 
the US cases are imported, and were not transmitted here. (The US data is 
distorted by the CDC's looser definition of a case.)

See the US Centers for Disease Control's SARS factsheet at 

You might consider buying some surgical masks.



>disease that they hoped to avoid. So long as they are isolated before they
>can infect other people, they do not constitute a meaningful local trend.
>Whether the isolation will be sufficiently prompt to prevent secondary
>infection is not yet known, especially because we do not know, definitely,
>if SARS can be transmitted during the incubation period.

More worrying is the possibility (not seen so far) that there will be 
people who can spread SARS *after* they get rid of clinical signs they have it.

Even more of a potential concern is the possibility that SARS might be able 
to jump back into a domestic animal (if it came from one) and spread that 
way as well.  Cats in particular are known to be highly susceptible to 
other Corona viruses.

Starting with the current 2500 cases and continuing on a ten day doubling 
time for 100 days would amount to 2.5 million people.  Another 100 days 
would see half the world's population infected.

I suspect, however, that 100 days might be enough to generate a vaccine.

>So far as I can see, the growth rate has been more or less arithmetic, not
>exponential; we do not have a measurable doubling time; and therefore we
>do not have an epidemic (yet). However it is a salutary experience to
>compare the sheer magnitude of the problem in Hong Kong with the
>situations in Canada, the United States, and Singapore. A fifth graph at
>my web site facilitates this comparison and illustrates that (for reasons
>which remain unexplained) Hong Kong cases have proliferated about six or
>seven times as fast as cases anywhere else. Thus the primary challenge
>seems to be containing the Hong Kong problem in Hong Kong. Whether this is
>possible will depend largely on political and regulatory issues.
>I conclude that for the time being at least, graphs of SARS cases are of
>no help whatsoever in predicting the future of the disease outside of

I hope you are right.  It makes sense that Hong Kong with its high 
population density could have problems unlike anywhere else.  For example, 
if people with SARS in the US mostly stay isolated at home and those who go 
to hospitals are treated carefully so they don't spread it to health care 
workers it might not be much of a problem in the US.

Keith Henson

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