Comment by tripletao

> Where do you see that? Where I live that isn't the case and according to official data the pandemic has never ended:

If those data don't show the end of the pandemic, then what would? Your confirmed deaths are around 1/100 of the death peak. Positivity fluctuates much less, in part because there's a feedback loop--authorities will test more if it gets too high (subject to resource availability), and less if it gets too low. It's well below the positivity peaks, though. In any case, if the plummeting death count were due primarily to plummeting testing, then we'd expect the test positivity to increase, and it definitely hasn't done that. I'm in the USA myself, with broadly similar trends.

> Governments were told by scientists that PCR testing has an FP rate of zero, so they just didn't build any processes to recognize the possibility or measure the error rate.

I don't know what the Swiss government did, but globally scientists certainly considered that possibility--for example, that's basically the point of all the papers comparing excess mortality against confirmed deaths. The agreement isn't perfect, but the trend is pretty clearly there.

> So? FPs are a problem regardless of when they occur or why.

Non-contamination false positives show up like an additive offset to the positive count, while contamination false positives show up more like a multiplicative scale. They're both bad, but the latter is usually less bad, since relative error is usually what matters.

> Nobody cares about detecting people who were infected months ago. Yet governments reacted to any positive test by assuming they were highly infectious and immediately forcibly quarantining the unlucky person who got it.

All governments that I dealt with were clearly aware that a positive PCR test didn't mean you were infectious now. For example, travel guidance generally permitted a recent (but not too recent) positive PCR test as an alternative to a very recent negative PCR test, since they knew that recovered patients might test PCR positive for a long time.

For people newly testing positive, governments didn't advise or mandate isolation because they thought the tests perfectly predicted whether a person was infectious now. They did so because those tests were the best tool available, and they judged the harm of missed isolation of infectious people to be greater than the harm of unnecessary isolation of non-infectious people. I agree that in many cases, that was a policy mistake. That problem is with the policy, though--the tests were performing exactly like any competent microbiologist would expect.

I'm not sure why your immunologist turned pale, since Ct cutoff around or slightly above 40 isn't unusual. For example, here's a pre-pandemic test for infectious salmon anemia virus that chose Ct = 42 in certain cases:

https://journals.sagepub.com/doi/10.1177/104063871102300102?...

In general, Ct values aren't comparable between different protocols. Sensitivity and specificity are judged from results on positive and negative controls, not from absolute Ct. There's no single best Ct; it's always a tradeoff between false negatives and false positives, and the weighting of that tradeoff varies with the intended use of the result.

> The Swiss government had a web page that stated point blank that PCR tests had no false positives at all.

That's clearly false. I don't think the American government said that, though they made other false absolute statements (if you get the vaccine then you definitely won't get sick, etc.). The consensus of the scientific literature told a much more cautious story, though.

It seems like your complaints are about the use of the PCR results, not the accuracy. If the PCR test correctly reports the presence of viral RNA, and based on that a patient is forced to isolate based on the x% chance they'd infect someone else, and you believe x is too low to justify that, then that's not a false positive; it's just a policy position that you disagree with.