This virus has been in the United States since December.
While there are a lot of people who think they had it when they had a bout of the flu - and as of last week, nationally the overwhelming majority of folks that thought they had it last week did not - there is yet to be evidence that it was here in any notable number, and plenty of evidence that it was not. The evidence is that some small numbers of infected may have slipped in as early as mid-January, just before the lockdown on China, with some more coming from Europe in February.