RE: MP response at last - & not the standard one6 Aug 2021 18:09
There's so much emphasis placed by folk on Ct number - It's really not relevant to focus so much on the absolute Ct number. "generally", <36 is regarded as positive, 36-40 as unclear, and 40 as the stop point. Depends a lot on how your known negatives look as well. Depends on amount of sample extracted, extraction kit used, amount of purified target used for the assay in question, PCR kit used, COV variant, inhibitors in sample etc - and none of the tests are quantitative. How the magical Ct number compares to "infectiousness" is a can of worms - no magic number that can tell that neither. Ct is a general scale to compare against - the higher the number from 1-40 the less amplifiable target was in the sample, correlating with amount of viral genome (in an ideal setting) but could be all dead or all super infectious. Impossible to quantitatively tie a Ct number to infectiousness though in anything other than general terms.