When I used to do RT-PCR for research, 40 cycles would mean (to me) that I had nothing in my solution and I had to redo the experiment. The precautionary princ

When I used to do RT-PCR for research, 40 cycles would mean (to me) that I had nothing in my solution and I had to redo the experiment. The precautionary principle (anti-scientific, because it assumes the worst even without evidence of such) is what drives such decisions, even if, according to Oxford's CEBM, there is little to no correlation between a PCR positive sample at 37+ cycles and actual presence of an infectious virus. That is why antigen testing, although less sensitive, is important. A PCR test without symptoms does not tell if you have the virus you had the virus, and if you are infectious (assembled virus present in the respiratory tract) or not. Also, RNA in the throat can degrade slowly, and be present for a long time (this is not unique to this virus). An antigen test will identify the virus proteins, and as such, a higher probability that a positive test detects an infectious virus.