The Analysis of Breathtaking Risk

With the frequent press reports of the probability of an epidemic of the so-called Swine Flu (the H1N1 virus) , I’ve been surprised that there has been so little published about how the well-publicized predictions are made.   Last month, however, specialists from University of California, Davis, the Washington (D.C.) Hospital Center, and a private consulting group published a research note about their risk analysis model that predicts the incidence of acute respiratory failure caused by the new flu.  If the disease is literally breathtaking, the predictions are figuratively breathtaking as well.
Before we get to those predictions, let’s this model into context.  It was essentially an operations management study for the benefit of hospital ICU directors–that is, what do ICUs need to brace for in terms of numbers of patients and the severity of their illnesses?  Although one commentary called the model a kind of "back of the envelope calculation" and this may be true, this model seems like a very necessary starting point.  Whatever its flaws, this research note should be an effective heads-up that will prod other epidemiologists to fire up the Monte Carlo software to refine the assumptions and the data selection.
Now to those numbers.  Although offering only a few details of their risk analysis, the researchers predicted that  
• 15 percent of the U.S. population will be infected with H1N1.
• 6 percent of those infected will require hospitalization.
• 12 percent of those hospitalized will ?? to acute respiratory failure.
• 58 percent of those patients who go into acute respiratory failure will not survive it.
The nod to the grim reaper in the last item amounts to total fatalities of nearly 200,000.  While this estimate doesn’t approach the 25 million fatalities in the flu pandemic of 1918, it’s still enough to take your breath away.

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