Monday, May 4, 2009

More Daily Flu-ness

(Visualization: Evan Robinson, Group News Blog; Data: WHO | Influenza A(H1N1))

Current WHO pandemic phase: 5
Laboratory confirmed cases worldwide: 1085 cases in 22 countries
Laboratory confirmed deaths worldwide: 26 in two countries
Laboratory confirmed cases in US: 286
Laboratory confirmed deaths in US: 1

As rapid testing comes online all over the world we're now seeing exponential growth in confirmed cases. If the exponential growth continues we'll see about 1500 total confirmed cases tomorrow and about 2500 2400 the next day. Since we don't have any real idea of how many cases might be out there but not confirmed, we still have no idea of the actual mortality rate. If we assume that the confirmation rate is identical for cases and for deaths (a dangerous assumption, but I think a relatively conservative one) then the mortality rate is about 2.4%.

Swine flu fears subside, but second wave looms correctly points out that earlier major pandemics involved several waves of morbidity with increased mortality in the fall and winter waves. If we dodge this particular bullet throughout May and June, we'll still have to worry about October and January.

Mexico appears to feel that the epidemic is winding down, while Canada has our first "severe" case. Janet Napolitano has pointed out that currently A(H1N1) "is not stronger than regular seasonal flu".

At this point I'm not too worried. As I've pointed out before, a typical flu season in the US averages about 36,000 deaths, and we've got 26 so far (.0007 times as many). We can, of course, see a rapid increase in cases and in deaths, but we may not, or at least not for a while. It's not time to panic yet. We are seeing tremendous acceleration in confirmation of cases, but we're not seeing a concomitant acceleration in confirmation of deaths. I believe that means we're seeing increased detection, not increased morbidity (sickness).

I've been reading The Great Influenza, and it's fascinating. I recommend it. It begins with a summary of the American medical education system in the 1800s, then provides an overview of the special conditions which contributed to the spread of influenza in the American army camps (the first known cases of 1918 "Spanish" flu were detected in Kansas). I'm looking forward to the rest :-).

[Updated 20090505 1245PDT: changed next day estimate from 2500 to 2400 after taking a more careful look at my graph -- the 2500 was just tossed off and I frankly didn't think the 1500 was going to be accurate enough to care about, but it was so I figured I'd better fix the mistake -- ER]