[skat20phys]

One thing about case reporting is that they tend to ignore the denominator, the number of tests.

I've been tracking DPH reports in our state since they started, and one thing I've noticed is that although the case counts have gone up, the probability of testing positive has remained roughly constant. It's increased slightly here in the last week or so but not a lot.

One thing this suggests to me is that at least here, the virus was present in significant numbers before they started testing, or at least in similar numbers.

If you combine that with consistent reports of substantial fractions of asymptomatic carriers, it seems very plausible to me that the virus was circulating before authorities in the US started tracking it.