Thursday, September 11, 2014

Conventional Wisdom And Epidemic Disease Spread

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# 9063

 

 

Not so very long ago (last spring, to be exact) the conventional wisdom was that Ebola was simply too debilitating, and too lethal, to have `legs’ . . . to spread beyond a limited geographic area.  Those infected were `too sick to travel’, and small outbreaks would inevitably `burn themselves out’  in relatively short order.


While a horrible disease, Ebola seemed fairly easy to contain.   At least, until this summer, when it wasn’t anymore.

 

Today Ebola is spreading – unchecked – in three countries (Liberia, Sierra Leone & Guinea) and has made inroads into two others (Nigeria & Senegal).  The number of infected is easily a magnitude greater than any outbreak previously seen, and the true extent of the outbreak isn’t even known. 

 

We’ve seen official estimates (and they are just that, estimates, based on incomplete information) from the World Health Organization that by the end of the year 20,0000 people could be infected.  When that number was first announced two weeks ago (see WHO Ebola Response Roadmap), it seemed an shockingly high number. 

 

Since then, we’ve seen estimates (again based on assumptions and incomplete data) that project potentially an even higher toll.

 

In Science Mag’s Disease modelers project a rapidly rising toll from Ebola, Christian Althaus of the University of Bern suggests that cases could possibly reach 100,000 cases by year’s end.  And his isn’t the highest number being bandied about.

 

Today, Science Editor Tom Clarke of Channel 4 News in the UK has published a blog called the Terrifying mathematics of Ebola, where he interviews Professor John Edmunds, an epidemiologist at the London School of Hygiene and Tropical Medicine – on just how bad this outbreak could get.

 

Keeping  Yogi Berra’s famous caveat in mind, that `'It's tough to make predictions, especially about the future.’, I’ll refer you to:

 

Terrifying mathematics of Ebola

Ebola treatment facilities in Monrovia, the Liberian capital, are now so overwhelmed they are turning away up to 30 infected people every day according the medical charity Medecins sans Frontieres.

Given the rate at which the virus is spreading, it says the virus will soon be having an “apocalyptic” impact on the country and its neighbours unless there is a dramatic increase in international assistance.

“It could get very bad indeed,” said Prof John Edmunds, an epidemiologist at the London School of Hygiene and Tropical Medicine. ”And I mean you can’t rule out some sort of nightmare doomsday scenario.”

(Continue. . .)

 

In this interview Professor Edmunds warns that the number of new cases is doubling about once every two weeks, and that Ebola has the potential to infect half the population of Liberia. Coming from a less credentialed scientist, that sort of speculation might be easily dismissed.  But not so, in this case.

 

While I’m not terribly comfortable with any of the projections offered to date, it doesn’t take a master statistician to see what a doubling of cases every two weeks  (or even every month) would mean. Granted, over the long run you’d run out of susceptible hosts for the virus, so you can’t extrapolate that progression forever. 

 

But in the short run, it can add up very fast.

 

Whether the `right number’  ends up being 20,000 or 100,000 or even more, the real point is we are in uncharted territory with this Ebola outbreak, and no one really knows where this goes from here. While I still believe that with a concerted international effort, this outbreak can still be contained, it is going to exact a heavy human and economic toll.

 

In closing, I would also note that over the past decade the conventional wisdom has also said that Avian flu viruses (like H5N1) couldn’t cause a pandemic unless they lost considerable virulence because – like Ebola - they are `too deadly’ and they `kill theirs hosts too quickly’ to spread effectively.

 

That’s the trouble with conventional wisdom. You can only take comfort from it up until the moment it no longer applies.

1 comment:

Don said...

"In closing, I would also note that over the past decade the conventional wisdom has also said that Avian flu viruses (like H5N1) couldn’t cause a pandemic unless they lost considerable virulence because – like Ebola - they are `too deadly’ and they `kill theirs hosts too quickly’ to spread effectively.

"That’s the trouble with conventional wisdom. You can only take comfort from it up until the moment it no longer applies."

Amen and thank you for saying it.