It's crazy how this has all changed travel to Italy within one week!
I think the pace that things are changing is only going to accelerate. In the USA, there has been nearly zero testing done until the last 24 hours. Now, suddenly (it would seem), there are cases popping up everywhere - because more widespread testing has begun. I suspect that in fact, infected people have been in the community for a while, it's only now that we have a tool to start discovering that, and we have been blind to the spread of the virus up until yesterday. Which means that it has been spread undetected for...who knows how long.
Locally, where I live, there has been the "discovery" in the past 24 hours of a half-dozen cases, one death, and another 50+ people who have definitely been exposed and are reporting symptoms - and only now they are now being tested. We'll see, but there's a good chance that there will be another 50+ cases documented here in the next 24 hours. The numbers are only going to go up.
I don't know to what extent (of any) the same "blindness" (due to lack of testing) has been evident elsewhere. But it seems clear (to me at least) that places that have not yet "discovered" infected individuals may have been enjoying a false sense of security, if they were not testing aggressively. We will see.