What is a CT value? CT stands for “Cycle Threshold” and indicates how many times a machine needed to try to copy a particular virus’s genetic material before being able to detect that material on a particular test called a Polymerase Chain Reaction (PCR) test. The CT value can be looked at as an indirect indicator of the amount of viral genetic material detected from a particular specimen on a particular test at a particular time. In general, a lower CT value indicates a higher viral load in that specimen, and a higher CT value indicates a lower viral load.
I have not heard of any other countries using this. If you test positive In the Cayman's, after 10 days in quarantine, your CT value needs to be above 32 before they allow you to get out of quarantine. I had no symptoms but my CT value started at 15, 7 days later it was 27, and when I hit 32.6 they allowed me to leave. I was not allowed out of my room. They set a table outside of my door where I could grab my food. I was told if I did not follow the rules of the government, I could be fines $10,000 and put in jail for 2 years. It was 12 days of hell. It was not cheap - $3000 for the room. So make sure you purchase insurance. Last minute flights are very expensive.