So we're left wondering what sparked this strange spread of human infection with a virus that is almost identical in its HA gene sequence from that found in birds and the environment during the outbreak (>99.5% amino acid identity; about 88% with H7N9s found in the US and Guatemala years earlier).
The strangest part is if it spread from birds.....why weren't vendors, traders, butchers and truckers in the closest of contact with the suspected hosts more commonly infected and reporting to hospital? Are they just too young? Too healthy? H7N9 infection seems to lead to severe disease most of the time. Did they have specific or cross-reactive immunity? Was the underlying disease factor the most significant issues for severe illness? We read in the literature that contacts mostly had no severe disease.
I guess we now wait to see what wild bird testing yields. Could wild bird populations already have H7N9 in them and be circulating in the Mediterranean and Australasian flyways?