Provided the testing strategy doesn't change (as the parent poster has stated may be the case), then it is a reasonable assumption that the testing is sampling

Provided the testing strategy doesn't change (as the parent poster has stated may be the case), then it is a reasonable assumption that the testing is sampling the population in the same way, day by day. So the important thing to look at is the growth rate. On that measure, it looks like the growth rate of cases in the US is outpacing that in Italy. That's worrying.