I wish I could find a "slam dunk" source that stated what the current threshold recommended by the CDC, but I can't quite find it. I've personally read many sources that talked about using cycle counts above 30 over the past year.

Some more discussion on this topic was on HN yesterday [0]

also, from last August:

  One solution would be to adjust the cycle threshold used now to decide that a patient is infected. Most tests set the limit at 40, a few at 37. This means that you are positive for the coronavirus if the test process required up to 40 cycles, or 37, to detect the virus. [1]

[0] https://news.ycombinator.com/item?id=27972195

[1] https://www.nytimes.com/2020/08/29/health/coronavirus-testin...