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[quote=Anonymous][quote=Anonymous][quote=Anonymous][quote=Anonymous][quote=Anonymous][quote=Anonymous][quote=Anonymous]For those who don't like the date of April, 2020, here's another article from infectious disease specialists from July, 2021:

https://www.usnews.com/news/health-news/articles/2021-07-14/why-covid-19-screening-should-be-used-sparingly-in-schools

Why We Shouldn’t Blindly Screen Students for COVID-19 This Fall
When case rates are low, the majority – and sometimes even the vast majority – of positive test results are false-positives.

The DESE testing program and others across the state and across the country have shown us that the probability of COVID-19 in asymptomatic students attending in-person learning was consistently low – less than 0.5% – even before widespread vaccination. [b]Using 0.5 as a (very) generous overestimate and a close-to-perfect (99% specific) diagnostic test, that means for every one true positive test, three will be false-positive. [/b]The true specificity of some polymerase chain reaction (PCR) tests is probably closer to 95% (in other words, still very good, but not quite so close to perfect). This more realistic estimate increases the proportion of false-positives test results even more – [b]up to 14 false-positives for every real case of COVID-19 identified by the screening program. [/b]As case rates continue to decline, the ratio of real cases to false-positives only gets worse (and worse). Assuming a rate of 1 in 1,000 or 0.1% and a nearly perfect test, there are 14 false-positive tests for every real case found by a screening testing program, and 71 if we use the more realistic estimate of 95% specificity.
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Thank you for posting this article.[/quote]

That article is pre-Delta and describes an environment of declining case rates.[/quote]

Delta doesn’t change math.[/quote]

Yes, it does. It changes the prevelance and also likely there are far more asymptomatic cases right now than there were before so prevelance is higher than we are thinking. [/quote]

And prevalence during delta in the UK was 0.63% (cite above in the thread), or about half that in primary schools (also cite above in thread).

That's "low prevalence" for the math of surveillance testing and false positives.

Also cited above, a test that has 1.5% of its tests be false positives + prevalence rates of 1.0% = 60% of positive tests are false positives

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Can this not be mitigated by always retesting? And or applying a traditional PCR test?[/quote]

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