But it's still true that most of the new strains of flu come straight from China, where they raise water fowl and pigs together, so the two species get to swap viruses back and forth quite merrily.
In fact, for a long time it was thought that the 1918 flu epidemic originated in Kansas, but further research once again puts it back to China. https://news.nationalgeographic.com/news/2014/01/140123-spanish-flu-1918-china-origins-pandemic-science-health/
To me the most interesting sentence is this:
Historian Christopher Langford has shown that China suffered a lower mortality rate from the Spanish flu than other nations did, suggesting some immunity was at large in the population because of earlier exposure to the virus.
That's basically the same reason so few old people in this country (and probably the rest of the world) even got that flu, let alone died: some fifty years earlier they'd been through an epidemic of a similar type A flu. And if the Chinese are in general a lot more resistant to flu because of steady, ongoing exposure, that's a bad thing for the rest of the world because to them influenza is a relatively mild nuisance, not so much a potentially deadly disease.
If influenza viruses were mutating in North American wild waterfowl populations and then getting loose in humans, it would be very obvious by now. There would be lots of outbreaks of very different flu types in North America. We just need to hope that our farmers don't take up a form of animal husbandry that puts the wild waterfowl in close contact with domestic pigs.
I find epidemiology totally fascinating. If you haven't had a chance to read
Spillover by David Quamen, do so. It's all about diseases moving from animals to humans, the conditions that allow that, and so on.
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