Saturday, 15 February 2014

H7N9 case announcements dropping: is Wave 2 under control? [UPDATED]

Its a very tough question to answer. There has been public pressure by China's poultry-farming groups on China to take measures to stem the industry's financial losses. These have been driven by the public concern that H7N9 can seriously afflict people and in about a fifth of recorded instances, kill them. 

And rightly so. The concern for those of us outside China is that reporting may be artificially halted, reduced or stemmed to calm the public - while doing nothing to stop the march of H7N9. This concern extends into thoughts about why we have so very few 2014 H7N9 sequences to date. Background for this paranoia about non-biological reporting limitations takes the form of :

  • MOA noting no evidence of H7N9 in poultry farms (1). Perhaps time to propose an alternative source then?
  • Poultry industry writing to demand that descriptors like "H7N9 bird flu" or "people infected with H7N9 avian flu" be changed to "H7N9 influenza" (2)(4). No argument from me there - bird flu is not part of the WHO nomenclature anyway. It's a media thing. Seriously though, will the name change the infections? Of course not. Same virus, same bird/poultry association with human disease. Call it Frank if you like but the process of infection, morbidity and mortality in 1:5 cases will go on.
  • Poultry industry groups asking Guangxi and Guangdong provincial governments to stop reporting each H7N9 case (3). Not acceptable and not addressing the problem at the source.

Click on image to enlarge.
Cases per day for all of Wave 2 (arbitrarily selected as
Oct-7-2014) and specifically for 2014. 

Orange and blue dots mark the rolling average
(each dot [data point] is the average of all data points
before it). The grey dots are the cases with illness

 onset on that day. The green bar reflects he current
laboratory turnaround time; the time between date
of illness onset and the date of reporting which we
hear about 2-3 days after the case is reported by
the jurisdictional Ministry. The pink bar indicates
that 2-3 day WHO delay period. Please allow for the 

fact that I am doing this from Australia which is 
ahead in time from the Northern hemisphere so my 
data are from "yesterday" and the x-axis extends into
a day you haven't had yet. The date the Hangzhou bird
markets in Zhejiang closed, my sentinel Province for a
market impact, is indicated. 
So, when we see a chart like this one, we may have those doubts at the forefront of our minds; more so than other reasons for what appears to be a constant decline in case reporting in recent days.

One such reason would be that the market closure (22-days ago for Zhejiang) and the laboratory reporting delay (currently 8.7-days for Wave 2) have finally caught up to the present day - and we are seeing a real impact of reduced exposure of humans to birds (poultry or market-based wild/song birds). 

As @influenza_bio (please follow him if you have an interest in flu - a real repository on influenza) noted on Twitter, it may also reflect a change in bird migration patterns. To me that that seems to be 2 coincidences in a row given a similar relationship between cases dropping and markets closing last year. The different could be that weather changes helped speed up the case decline in 2013. Maybe.

None of you reading this (since I believe the blog cannot be accessed in China) know the actual reason for this decline. 

In the absence of any other data or a change in climate, I'm proposing that the case decline to a direct effect from the market closure. If that hypothesis is correct, we will see continued decline in cases in Zhejiang and wherever else markets were closed. 

That decline in total H7N9 human case announcement began 3-days after Hangzhou markets closed. Given that most cases were accruing from Zhejiang province, I still think that's a good place to watch.

  1. Xinhua story.
  2. Xinhua story (needs translation)
  3. South China Morning POst
  4. China Animal Husbandry Association

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