This virus has most likely been circulating for some time, in the same way that they established that HIV had been around since the late 1950s.
It had evidently been circulating in Washington State for some time, as there was already community transmission at the time that CDC was restricting the diagnostic tests.
And another thought - we were in New York and Washington for a couple of weeks in late October last year and my wife ended up with a pneumonia that didn’t go away and she had several courses of antibiotics, which didn’t assist, so it was presumably viral. Cough, sore throat ... took ages to resolve.
Back in 2009 the swine flu was circulating in Melbourne’s northern suburbs long before the State authorities realised - and this article about the DHS’ response is sadly prophetic in many ways:
The general practice experience of the swine flu epidemic in Victoria — lessons from the front line | The Medical Journal of Australia

