Monday 4 May 2015

The third outbreak of influenza A(H7N9) virus seems to be over...

Cumulative curves of reported H7N9 cases and deaths in humans.
Click on graph to enlarge.
By the looks of the curve on the right, the rush of cases that defined the third known outbreak of the low pathogenicity avian influenza A virus subtype, H7N9, is over...for another season anyway. 

If we get into the nitty gritty, as I have below, there are a couple of interesting things to see. First though - let us remember that these are just reported data:

  • there may have been some cases that were not reported for whatever political, medical, social or personal reasons - these data are an idea of what happened - look at the rends and don't get hung up on the specific values
  • the overwhelming majority of the cases have reported to a healthcare facility with respiratory disease due (presumably) to either infection - we have no idea how many other people have been infected, what proportion were mild or asymptomatic (as I've discussed e.g. here and here, so we know it is possible). It could be half as many again, or 100 or 1,000 times as many.
  • these are only cases that have been examined with a laboratory test (as far as we know) - there may have been many other cases of "influenza-like illness" that did not get sampled and tested but were managed under (or not) the assumption that they were influenza of some type, subtype or strain.

Please note-the graphs used here can all be found on my fixed interactive H7N9 page at:

The interesting stuff includes:

  • For the 2 outbreaks we have continuous data for - 2013-14 and 2014-15, the start of the outbreak seems to be around October/November, with the peak around January/February. 
  • Outbreak 3 did not seem to reach the heights of the preceding year however, from what we could glean from pretty poor data, the link to poultry exposure was as strong as ever. Perhaps market closures in response to deaths were a little more effective/efficient/wide-ranging in Outbreak #3? Pure speculation

Click on graphs to enlarge.
  • Most of the cases in 2015 (bottom maps) were on the east coast of China

Click on map to enlarge
  • Most of the activity in the 3rd outbreak was focussed in Guangdong, Fujian and Zhejiang provinces (the red ones above) 
  • Xinjiang Uyghur Autonomous region (in the far west) and Guizhou and Hubei provinces joined the list of host regions in Outbreak #3
  • Xinjiang joined Guangxi and Jilin provinces (which reporting cases in Outbreak #2) as regions of China that share a border with another country - heralding the movement of this H7N9 variant beyond China's borders possibly into Vietnam, North Korea, or a -stan
Click on graphs to enlarge.
Keep an eye out for H7N9 Outbreak #4 - coming to a colder China around November 2015. 

But for now, it might be time to hit the FluTrackers line lists (okay, I've had 4 tabs open for ages) and graph the course of another source of concern - H5N1 cases in humans.

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