Now we know:
An F.D.A. spokesperson said home collection kits raised additional concerns about safety and accuracy that required the agency’s review. The issue in the Seattle case appears to be that the test results are being used not only by researchers for surveillance of the virus in the community but that the results are also being returned to patients to inform them.
The two kinds of testing — surveillance and diagnostic — fall under different F.D.A. standards. In a pure surveillance study, the researchers may keep the results just for themselves. But coronavirus testing has largely revolved around getting results returned to doctors who can share the results with patients.