Risks of false positives in school testing with Innova
Innova testing of asymptomatics in England has very low rates of test positivity at the moment (0.3%). The lower this figure gets, the more likely a positive result is to be a false positive than a true positive.
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Innova testing of asymptomatics in England has very low rates of test positivity at the moment (0.3%). The lower this figure gets, the more likely a positive result is to be a false positive than a true positive.
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This rate is in health care workers and others getting community testing – you will expect rates in school testing to be lower as children have been locked down.
What are the chances of a positive result being a false positive?
Best data we have are from University testing
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What are the chances of a positive result being a false positive?
Best data we have are from University testing
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Kudos to @PubHealthScot for looking at this with University students and clearly and fully reporting their findings.
Excellent weekly reports are on their website
beta.isdscotland.org/find-publicati…
Report from 27th Jan shows key data for Uni testing in Nov/Dec.
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Excellent weekly reports are on their website
beta.isdscotland.org/find-publicati…
Report from 27th Jan shows key data for Uni testing in Nov/Dec.
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Data up to 17th Dec found 106 of 49904 positive (0.2%).
The majority (must be around 70) of which were at Dundee university. PCR testing of positives here showed a very high false positive rate and it was determined that the University had a received flawed batch.
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The majority (must be around 70) of which were at Dundee university. PCR testing of positives here showed a very high false positive rate and it was determined that the University had a received flawed batch.
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From the other unis data to the 19th Dec found 35 LFT positives and 45505 negatives (0.1% positivity rate)
Of the 35 positives, 25 were confirmed positive by PCR, 10 were negative on PCR. So positive predictive value is about 70% (95% confidence interval from 55% to 85%).
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Of the 35 positives, 25 were confirmed positive by PCR, 10 were negative on PCR. So positive predictive value is about 70% (95% confidence interval from 55% to 85%).
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So without PCR confirmation ...
... Dundee would wrongly think it had an outbreak
... about one third of those isolating (don't forget their contacts as well) would be doing so unnecessarily.
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... Dundee would wrongly think it had an outbreak
... about one third of those isolating (don't forget their contacts as well) would be doing so unnecessarily.
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Suggests that PCR confirmation for schools testing is absolutely essential to ensure only real cases and their contacts are isolated – why is it not organised?
(also you might start asking questions as to when levels are too low for this testing to be worthwhile at all).
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(also you might start asking questions as to when levels are too low for this testing to be worthwhile at all).
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