False positives exceed true positives.
Indeed they do. Today, updating my spreadsheet, we have 1.42% Cases/Tests. If my assumption that the recent curve flattening at 1.4% for the last week represents actual false positives, this does indeed mean that ALL the reported cases are false.
Of course, as I said, it is a bit too early to state this with confidence, but it is beginning to look this way. It certainly needs to be monitored.
False positives exceed true positives.
Indeed they do. Today, updating my spreadsheet, we have 1.42% Cases/Tests. If my assumption that the recent curve flattening at 1.4% for the last week represents actual false positives, this does indeed mean that ALL the reported cases are false.
Of course, as I said, it is a bit too early to state this with confidence, but it is beginning to look this way. It certainly needs to be monitored.
I doubt one can say anything with total confidence.
But I think it unlikely that false positives are running as high as 1.4% of those tested. The usual level cited now is below 1% of those not infected. Crudely that might mean, say, out of 10,000 tested, 14 test positive of which 9 are false and 5 are real.
But the spread of realistic scenarios will be wide: 14 positive results could realistically range from (a) 14 false positives to eg (b) 4 false positives and 10 true positives.
With positive tests as few as these, one can individually retest/observe those who test positive.
The letter by Healy et al (Microbiology & Infectious Disease, Swansea Univ Hosp) is v. useful https://www.bmj.com/content/369/bmj.m1808/rapid-responses
They had 31 PCR positives to follow up, as identified on 3 different systems, each of which sought SARS-CoV2 by looking for 2-3 gene targets.
26 of the positives had only had one of these genes detected in the original PCR, and so were iffy, especially as CT values were high (suggests v. little gene detected).. 19 were retested, and all were negative. Some of the 26 had symptoms but repeat tests were negative... perhaps they had some species of common old.
5 were positive for 2-3 of the target genes sought, which ought to be a better pointer to true SARS-CoV2 infection. One developed symptomatic infection, one had evidence of old infection and 3 were asymptomatic.
Hancock et al need to be pressed to say what they are now calling 'positives'. Are these people in whom one gene target has been found in one test? If so, both the statistics (as analysed by Carl Heneghan, Dr Yeardon & others) and the above practical experience suggest false positives are apt to outweigh true 'risk' positives, probably by a considerable factor.
Such positives need to be checked by a second independent method and lab, they should not be the basis for incarcerating people and their contacts unless they are part of an obvious cross-infection cluster from a single event.
I write from the basis of a 40 year career in microbiology.
David,
This is very significant. Thanks.
Hancock et al need to be pressed to say what they are now calling 'positives'. Are these people in whom one gene target has been found in one test? If so, both the statistics (as analysed by Carl Heneghan, Dr Yeardon & others) and the above practical experience suggest false positives are apt to outweigh true 'risk' positives, probably by a considerable factor.
This is now urgent.
I write from the basis of a 40 year career in microbiology.
Thanks for your knowledgeable input, David. Can you, or anyone, comment on my two suggestions from my chart above:
This is crucial to sort out. You can see the sinister implications of the second suggestion.
