H7N9 outbreak #3 underway?

What better way to start 2015 than a snapdate!! For those who are new to them here on VDU, they were initiated here and defined here as snap updates - posts that don't have lots of detail and chat...although they almost always end up having lots of chat!

Figure 1. H7N9 cases by week of onset (or hospitalisation
or reporting dates of the preferred onset date was
not made public).
Click on image to enlarge.

This one is an update of the situation of one of the many avian influenza viruses ("bird flus" if you must) around again - avian influenza A(H7N9) virus, or just 'H7N9'.

In Figure 1, I've taken the huge liberty of adding in the start and end dates of the 3 outbreaks of H7N9 to date; and in doing so, I've said that China is in the early stages of one right now. I may well be wrong of course - this is a blog and these are my opinions - but it looks that way to me. 

Figure 2. China's northern laboratory network influenza
surveillance data up to Week 51 of 2014. [1].
Click on image to enlarge.

The case numbers for H7N9 in Figure 1 have been above zero for a little while and in particular November looked like a busy month (see weekly and monthly tallies here). Keep in mind that there is also a reporting lag - the time between date of onset (obtained from more detailed World Health Organization data) and the date the case was publicly reported (I rely on FluTrackers line list for these details). That delay can be a month or more on occasion; up to 38-days in late December. I suspect this is because China reports cases to the WHO in batches, something instigated toward the end of the 1st and 2nd outbreaks. So I suspect we will see more cases assigned to December, during reports that come out in January.

But it look like 'tis the season for influenza in humans in China (see figure 2 and the Chinese National Influenza Centre [2]) - and as some of us have discussed on Twitter, this is most probably due to the changes in weather (environmental conditions) which result in sustained viral survival on cough and sneeze-contaminated surfaces and in wet and dry propelled droplets and droplet nuclei; in both man and bird (see Hong Kong avian influenza detection report dates [3]). 

That sustained survival may well be all it takes for more of us to pick up an infectious viral dose.

Once the seasonal influenza viruses get a foothold in us, they spread well, causing disease in those who are susceptible and probably a bunch of unnoticed infections in those with previous exposure to that strain plus a healthy immune memory of that intrusion. By "seasonal influenza virus, I mean those that replicate in and circulate efficiently among humans, as opposed to the relatively inefficient avian subtypes.

So stay tuned to H7N9; it's not yet very good at spreading between humans but its established in birds and has been spilling over into humans since at least the beginning of 2013. We know how influenza can deal us a rough hand if the stars and its genetic segments align favourably (for it). Oh, and the continued reliance on fresh chicken obtained from and killed at live poultry markets. The majority of cases have very clearly had contact with poultry as defined by the WHO. 

References...

1. http://www.cnic.org.cn/eng/show.php?contentid=738
2. http://www.cnic.org.cn/eng/surveillance.php
3. http://www.chp.gov.hk/files/pdf/global_statistics_avian_influenza_e.pdf