> In this paper they've used 45 for HIV. What's your point?
There is a difference between HIV vs SARS-Cov2: If you get AIDS, your body does not have the capacity to recover from it on its own. So, 1) the chances of detecting dead material from a long gone infection are nil; and 2) the cost of a false negative is much higher than the cost of a false positive.
Since most people seem not to be seriously affected by a SARS-Cov2 infection, neither is true for SARS-Cov2. So, not agreeing on a fixed, reasonable, standard number of cycles which everyone uses has the consequence of inflating false positives for no gain. Note WHO's updated information[1].
> WHO guidance Diagnostic testing for SARS-CoV-2 states that careful interpretation of weak positive results is needed (1). The cycle threshold (Ct) needed to detect virus is inversely proportional to the patient’s viral load.
If you are not sick and your viral load is barely detectable, what's the point?
So you think they should use some lower Ct number for which it would be possible to show that eg 99.5% of people who are over it (i.e. have lower viral load) don't infect anyone? Interesting. I've read that most of the false negative for a PCR test actually come from sample collection (makes sense, PCR is super reliable) so it could be that you would miss people with high viral load where the sample was just not taken in a perfect way. Especially early in the infection it could be quite localized.
> So you think they should use some lower Ct number
Everyone should use the same number in all tests. From what I understand, about 20 is a reasonable number which might still result in positives up to a month post-infection. I consider having a standard more important that the specific number chosen. It seems when people go to > 30 it is in a quest to ensure a positive test result.
https://www.hindawi.com/journals/art/2016/7954810/