Yesterday I blogged about the age distribution of (A)H1N1 and the observation that younger age groups are being affected disproportionately. I graphed the reported cases against the population distribution by age and showed that result. But I levelled a number of criticisms at this analysis. Young people might be more prone to catching Swine Flu for lifestyle reasons, for example, rather than anything innate. I commented that a better set of stats to look at would be how this virus compares to previous seasonal flu outbreaks.
And that’s just the set of stats that NSW Health have, in their July 15 Epidemiological Weekly Report. You can read the whole report here. Towards the end of this report is a great graph, reproduced below:
What this graph shows is the age distribution of cases admitted to hospital with 2009 H1N1, compared to the average age distribution of cases admitted to hospital in 2004-08 with “normal” seasonal influenza. And the graph shows an interesting thing. In the sparse language of the report:
The data confirms a shift towards young and middle-aged adults in those admitted to hospital with H1N1 influenza 09, compared to those admitted to hospital with normal seasonal influenza over the previous 5 years.
It’s teenagers and young adults who are being disproportionately seriously affected by Swine Flu, compared to the normal seasonal influenza experience. This, I keep hearing, is typical of new flu pandemics. No-one seems to be able to clearly explain why. There are some theories (such as the “cytokine storm” in young peoples’ immune responses) but that’s the subject of another post some time.