In fact, we have no evidence that affected people could transmit the virus to other species, including birds. The highest risk of virus introduction is uncontrolled live poultry trade between affected and unaffected areas.But absence of evidence is not evidence of absence.
We have seen studies, like this one, that use a human H7N9 virus and use it to successfully infect chickens. So the virus is capable of replicating even if it is inefficient at spreading to other chickens or even ferrets ( a human surrogate of influenza infection). But then we do know that humans get infected from exposure to something in poultry markets.
I agree (for what that's worth), that the risk of spreading virus is more in the area of moving infected birds around, as well as their own migration movements. But I think it is too early be early to issue strong denials that humans may infect poultry until we find some data to support them.
Sources...
- CIDRAP article.
http://www.cidrap.umn.edu/news-perspective/2014/02/china-reports-one-h7n9-case-fao-says-human-illnesses-arent-threat-poultry - H7N9 transmissibility article
http://www.sciencedirect.com/science/article/pii/S0042682213006855 - FAO statement
http://www.fao.org/news/story/en/item/214244/icode/
