The news has been returning to swine flu over the past week with the WHO declaration that it is now a swine flu epidemic and that Scotland was experiencing many cases. I've been monitoring the available data from the WHO and the UK Health Protection Reports and feel that sufficient time has passed to provide some visusal data giving a possible insight on whether conrol measures are working, in the form of graphs.
The results suggest the following conclusions:
- The rate of new infections apparently slowing down in Mexico
- Control measures are having an effect in the USA and world generally in that the rate of new infections is only increasing linearly, as opposed to exponentially.
- Surprisingly, the UK is showing an exponential increase in the rate of new infections. Looking at the nations and regions, it appears that England's rate of increase is almost linear, with Scotland having shown an exponential increase over the last three weeks, which could explain the UK figures.
Looking at the wealth of information for winter flu and other flu epidemics, the curves created by data on numbers of confirmed infection show an approximation to an S curve. That is, infections increase exponentially (in a rising curve when plotting total infections against time) until levelling off to a tailing peak. This is how I show the data in my graphs. In a winter epidemic, this takes over circa 24 weeks.
If you plot the number of new cases against time over an epidemic, you get an epidemic curve which has a typical bell shape.
So assessing whether control measures are effective can be seen in two ways; 1. a slower rate of exponential increase during the first half of the S shaped infection curve 2. a lower peak of total infections.
We are only 6 to 8 weeks into the pandemic. It was therefore very gratifying to see that the USA and World graphs did not show the strong exponential increase in infection cases expected in an unregulated epidemic. Instead, the increases show a steady linear increase. In Mexico, there is even an indication that the epidemic is tailing off.
The exponential increase in the UK was therefore a surprise, even though this is predominantly due to the increases in Scotland over the 2 weeks before 12th June. However, we should bear in mind that the numbers of cases could still be a much lower figure than if no control measures had been introduced and also that we see significant changes for the better over coming weeks.
I'm not panicking! But I'm keeping my eye on the situation.