My understanding is this hasn't been done yet because we still don't have enough tests for all the people who have symptoms or might have the disease due to circumstances. But the number of available tests is going up very rapidly, so maybe pretty soon we will be able to do that sort of study.

Of course, our stable genius president has been insisting for months that there is no shortage of tests.

By the way, another way to go at this question is to test for antibodies, and that is also being developed very rapidly.