Wednesday, June 10, 2009

H1N1(aka American flu) spread

I just came across this interesting set of graphs (Wikipedia) showing the spread of H1N1 globally. BTW, I still believe it should be called the 'American flu', cos H1N1 is confusing since there are so many H1N1s around.

Note the 2 front runners, Mexico and US. So it should be American flu, should it not?

Incidentally the graphs are on a semi-log plot which means that a straight line would represent an exponential rate of growth. What we can see is that all the plots are biphasic, meaning they have at least two slopes - and initial rapid exponential growth which then flattens out to a slower growth. I guess this means that either the virus loses steam, or that more extreme control measures in the community begin to take effect.

What should be noted also is the divergence of the infection and the death plots. A month ago, total deaths were approximately (hard to read off a semi-log plot) 1.2% of total infections, but now it is less than 1% (closer to about 0.55%).

This graph on a linear plot shows the divergence clearer.


qiufen said...

why "american flu", not " mexico flu" meh?

gigamole said...

It's the Americas mah....

Anonymous said...

The virus is neither losing steam, nor are extreme control measures taking effect in the countries that matter, except perhaps Mexico. What you see on the charts is basically an artefact caused by countries (like US) which have essentially stopped testing all but hospitalized cases, as well as countries (like Philippines) that do not have the resources to test all suspected cases even if they had wanted to do so.

gigamole said...

I don't know, Anon. Every curve there is bi-exponential. Can't be every country generating artifacts.

Anonymous said...

Don't look at just the wikipedia charts, look at the individual country/region's reports online. Useful sites would be fluview (CDC) or EISS (Europe). Although US influenza cases have not exceeded the epidemic threshold, > 80% are now caused by the new H1N1 virus. Ditto for Europe. It is normal for influenza figures to fall in summer, but to rise in winter (which is happening for Australia). WHO should be declaring this a pandemic very soon. One should not conclude from the virus' lack of virulence (which may still change either way) that there are issues with transmissibility. This H1N1 virus will probably circulate the world for another couple of years at least before it becomes yet another "seasonal virus".

gigamole said...

I'm not really sure what you're saying, Anon.

True, Wikipedia isn't great science, but I am not sure all that detailed number crunching at Fluview and EISS is telling us anything that the Wikipedia isn't telling us.

Yes, the virus is transmissable. No one doubts that. But the charts tell us the speed of spread tends to slow down quite soon after it hits the community. Why, isn't very clear at the moment. It happens in every chart.

And there is no indication that the virus has any teeth at the moment. Maybe it will reassort at some future date, and return with a vengeance. But then again maybe it won't.

So WHO has declared a pandemic. I am not really sure what it means. Technically they are right. But what are we supposed to do now?

Aren't all the seasonal flus pandemics in their own right?

Anonymous said...

That's the trouble with just looking at Wikipedia charts without realising what's happening in the countries with community transmission of the virus. The speed of spread appears to slow down far sooner than in reality because the intensity of testing drops in most cases. Even in countries like Japan. After a while, it just becomes pointless to try to test and capture every single case.

What something like fluview tells us in addition is how many influenza-like illnesses are being picked up at different sentinel sites (and whether this is above or within the historical average), and of the proportion sampled, what percentage is now due to the new virus. So what we see now is that the new H1N1 virus is replacing (but fortunately not quite additive to) the seasonal influenza viruses quite quickly.

gigamole said...

Fair 'nuff.

But doesn't that just tell you the novel H1N1 is more transmissable than seasonal H1N1 and that perhaps some cross 'immunity' is present so that novel H1N1 infections somehow mitigate against season H1N1? This may be the reason why older the virus affects younger people.

So now that this is a 'real pandemic, the solution is to step down control and up mitigation?


We should have done that earlier. The virus is unstoppable. The epicentres do not make any effort to control spread, and continue to export the virus.