Tuesday, 14 January 2014

H7N9 age with time: is a younger adult demographic emerging this time around?

This is a big graphic - sorry for that - but I thought it best to show the distribution of age bands (this is updated from the paper I co-authored recently with Joseph Dudley) alongside the shifting age in total numbers and proportion of cases each week. The data are all publicly sourced and verified against the WHO and scientific literature whenever possible and of course, against FluTrackers excellent case list.

1 case is lacking age data.

The chart below (click on it to enlarge and see much more clearly) then some comments underneath. Keep the previous sex/week chart in mind (it's trend has not changed much with the latest cases; these charts also result from a question from CIDRAP's Lisa Schnirring last Saturday) when looking at this. Is any effect seen below due to the increased female representation?

Click on image to enlarge.
It's probably more technically correct to use a line graph for (c) 

since a linked line implies that we know what happens in between 
each data point, but bars just don't show up clearly enough.

  1. The median age of all H7N9 cases (surviving and fatal) is currently at 59-years; the mode is at 54-years.
  2. The median age since Week 33 (see earlier post for why this number) is 54-years whereas from Week #1 to Week #32 it was 60-years. Is this a significant lowering of the median age in wave 2 or just because we're coming into Marc-April, where things may even out?
  3. 74% of all cases are aged 40-years or older (M:F 1:2.36); 48% are 60-years of older (M:F 1:2.23); 6% are 20-years or younger (M:F 9:1)
  4. The age band graph (a) looks very similar to that which we published in late 2013 using 136 avian influenza A(H7N9) virus cases (not at 175 cases)
  5. The total numbers in graph (b) show that patients 20-years of age or younger have not yet shown up among the new wave of H7N9 cases, and if we look at the proportion of each age band each week (c), we can see that a younger than 60-year old demographic is predominating from December, as it did back in March and April 2013.