Monday, April 27, 2009

Swine Flu

Well, it looks like there is a case in Northern California now. Joy!

It is unclear, when the numbers are so low, what will be the size of the epidemic and what will be the mortality rate. The rate of 173 death out of 1,995 infections would be alarming if we really knew that 1,995 was the correct denominator. However, there is likely to be considerable under-ascertainment in a country like Mexico among the survivors (especially those who did not seek medical care). This factor is likely to be especially important if reports of patients being turned away from medical care turn out to be widely true.

On the flip side, with only 40 cases in the US, many of which may be at the beginning of the course of the disease, we have no idea what the mortality rate is likely to be. It is still possible for it to be 0%; at which point we'll look like we over-reacted.

I think that this is a good example of the challenges of problems with lagged information (incubation times) and geometric growth rates. The point at which intervention can be effective seems to also be the point at which there is not enough data to distinguish a serious public health issue from a decidedly mild outbreak.

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