On his VDU's blog, Dr. Ian Mackay writes: Neither market nor farm poultry very positive for H7N9; songbirds the the culprit...? Excerpt and then a comment:
Following on from yesterday's post, "If not poultry then what?", I thought it worth noting the impressive numbers from the Chinese Ministry of Agriculture.
• 1,630,000 poultry and environmental samples tested
• 88 POS; all from live bird markets• None from poultry farms
From 2014, to date:
• 33,400 poultry and environmental samples
• 8 H7N9 POS; all from live bird markets• None from poultry farms
The other alternative to answer the question in my heading; the testing methods are at fault.
No detail of what approach has been used to obtain these numbers in the links below. Viral culture and serology with some PCR have been noted before. I'd wager culture yields chicken scratchings compared to PCR for detecting virus in the wild; but serology has successfully been a pillar upon which animal testing rests. So that's why the numbers above are such a quandary for the epidemiologist who reads about the high frequency of links between human disease and exposure to poultry.
It would be nice to see some technical papers on antibody test testing (development and validation) at some point.
I keep wondering about the statistics of H7N9 as well. In a nation of 1.3 billion hearty eaters of billions of chickens, how is it that so few people come down with H7N9? Why do the authorities find H7N9 in one of two places: in the victims, and in live poultry markets?
We know that a bird crawling with H7N9 will look you in the eye and seem perfectly healthy, so could it be that far more of them are carrying H7N9 than we have so far found? And are far more people catching mild or even asymptomatic cases than we realize?
I have no idea. But the striking aspect of both H7N9 and MERS is that even after months of intensive research, we still don't really understand them.