Daily Testing in school study report is out but presentation by BBC here is SPIN SPIN SPIN

The trial failed to show convincing reductions in school absence, and could not rule out large increases in Covid transmission. Sensitivity of the test was 53%.

bbc.co.uk/news/health-57… The preprint for this study is here. Not yet peer reviewed.

modmedmicro.nsms.ox.ac.uk/wp-content/upl…

SO what’s this POSITIVE news about medical tests?

Said it would be Monday, but actually the news broke this afternoon. So an early release from my tease …

Thanks for sharing your hopes about what it might be … I enjoyed many of them … but none were that close.

1/10 For me, positive news would be knowing

1) High quality tests are developed using the best expertise from industry and universities

2)Tests are evaluated in strong robust studies to work out whether they work in the real world for the purposes to which they are put

2/10

This new study suggests LFTs in primary care have sensitivity of 95% and specificity of 89%, but it is FLAWED.

These results are misleading because of PARTIAL VERIFICATION BIAS

A quick lesson ….

1/9
sciencedirect.com/science/articl… Participants were first tested with LFTs – 810 positive and 1736 negative. The investigators choose to test 217 of the 1736 negatives with PCR – that’s 1 in 8. This wasn’t a random sample as they were influenced by clinical characteristics as well as the test result.

2/9

Even more data on LFTs out today.

@dhscgovuk released report of studies of Innova and Orient Gene, and their interpretation of findings.

Includes unpublished studies

BUT Clear evidence of post hoc interpretation of results based on naïve definition of infectiousness.

1/10 Long link is here:

gov.uk/government/pub…

2/10

Results from the LIVERPOOL EVENT PILOTS have been published on line and in the media. Somehow I missed these coming out. cultureliverpool.co.uk/event-research…

No official report from @dhscgov as per normal.
Seems important evidence is being delayed once again.

1/7 The bottom line is that the events were safe.

Kudos to Liverpool PH Team.

But detail is interesting to see why they were safe.

2/7

What do we known about ORIENT GENE used in the Daily Contact Testing Trial by the @educationgovuk and @DHSCgovuk?

There have been claims that this test is as good as others and has been reviewed by @MHRAgovuk for use in assisted testing. This is not right

1/10 The process does not make sense.

The MHRA never review products for assisted testing as they are professional use tests, which go through the self-certification process to get a CE-IVD mark.
MHRA doesn't go near this process.

2/n

IMPORTANT: MHRA New standards for LFT self tests for SARS-CoV-2 in people without symptoms.

@MHRAgovuk just published new Target Product Profile.

This is a guidance document based upon the best available evidence and independent expert opinion.

1/12

gov.uk/government/pub… Important to note that the MHRA see these tests as for detecting “Current Infection”. That is detecting active infection, but is bigger than checking whether people are infectious. It also includes people who are pre-infectious.

2/12

The 1st 2 weeks of school testing did find MORE FALSE POSITIVES than TRUE POSITIVES - data are finally public.

Proportion false were 62% and 55% in these 2 weeks. Of 2304 positive tests, 1353 were likely false, with 1 positive per 6900 tests done. Remember that the law made kids, teachers, families and bubbles had to isolate for 10 days even when the PCR came back negative, despite the @RoyalStatSoc spending days trying to explain the issues to @DHSCgovuk.

Never ever say tests don't do harm.

Well here is some real data from 27 health care workers who picked up symptomatic Covid-19 infections whilst being tested twice weekly using RT-PCR. The paper develops models to look at impact of testing frequency, but also hypotheses on LFT performance
bmcmedicine.biomedcentral.com/articles/10.11… There is excellent presentation of the original data in the paper, as well as results from the models. Kudos to the authors.

Plots of Ct values from PCR are provided, which show that RT-PCR with Ct<37 had a peak sensitivity for detecting infection of 77% 4 days after infection.

For the sake of clear Public Health messages, listening to this interview on @theJeremyVine I'm tweeting some responses to the claims made by Peto

https://twitter.com/deeksj/status/1383168237911871490

#1 "the lateral flow test has the remarkable ability of only picking up people who are likely to be infectious, or other words a danger to others."

Senior staff at Department of Health have concerns that Mass Testing needs to stop ...

Great article from @JoshHalliday

Rapid Covid testing in England may be scaled back over false positives theguardian.com/world/2021/apr… From leaked emails ....

Ben Dyson, an executive director of strategy at the health department and one of Matt Hancock’s advisers, stressed the “fairly urgent need for decisions” on “the point at which we stop offering asymptomatic testing”.

Take note - @dhscgov rapid tests are being sent out (certainly in schools) with two different (and conflicting) information sheets, one in the box and one given out separately.

(the crumpled one with the picture is in the box, the glossy one is handed out separately).

1/10 The clue to which one is most up to date is on the back page (the one in the box is the out of date version).

2/10

@drdavideyre isn't the 89.5% figure based on the samples in symptomatic index cases taken at the test-and-trace centre? So this shows how good the test works in those who attend test-and-trace with symptoms? Pretty good idea to use them there.

https://twitter.com/drdavideyre/status/1379085356700602375

Using this test (or better ones) backed with PCR in test-and-trace centres could revolutionize contact tracing- if people get their results and meet with an infection control team before they leave the centre we will be moving everything forward 3 days. Add in financial help too.

Important paper in @bmj_latest from global leaders in test evaluation. Hope will improve quality of studies.
1/n

Guidance for the design and reporting of studies evaluating the clinical performance of tests for present or past SARS-CoV-2 infection bmj.com/content/372/bm… Thanks to @JennyDoust @KatyJLBell @leeflang_m
@jacdinnes @SallyJLord @SueMallett Janneke van de Wijgert, Sverre Sandberg, Khosrow Adeli,@pmmbossuyt Andrea Horvath for working on this with me. Its a team which covers all important aspects of test evaluation.

2/n

ONS just announced weekly infection rate in secondary school aged children is 0.43%.

Yesterday Test-and-Trace data showed 0.047% of LFTs were positive.

How can we get an estimate of the sensitivity of LFTs from this? I’ve come up with sensitivity=10%

Here are my workings Three issues

#1 0.047% will include LFT false positives – 0.03% according to DHSC, so 0.017% will be LFT true positives.

#2 0.43% will include PCR false positives – lets go for 1 in 1000 (probably less) to be conservative. So 0.33% will be true cases

LFT test results for week to 17th Mar

Flatlining – few cases in schools - costing tons of money - causing many FPs

7.6M tests week, up from 6.3M
@£5 per test=£38M
@£20 (real cost reported from Wales)=£152M

To get 8279 +ve results (0.108% yellow line) many of which will be FP What happened in secondary schools?

3.9M tests in students, 1805 positive results.

1 in 2140+ve (previous week 1 in 2070).

Would expect 1160 false+ve if 99.97% specificity (Government’s new claim)

64% of +ves were false+ve with kids+bubbles+families isolating unnecessarily

Updated @cochranecollab review of Rapid Tests for Covid-19 is here

Rapid, point‐of‐care antigen and molecular‐based tests for diagnosis of SARS‐CoV‐2 infection - @jacdinnes @deeksj - 2021 | Cochrane Library

cochranelibrary.com/cdsr/doi/10.10…

1/12 Update included electronic searches to end of Sept, and other resource up to mid Nov 2020. Next update is already underway. Many thanks to the great crowd of people involved in putting this together.

2/12

More disappointing data on sensitivity of LFT for mass testing - this time from Wales.

This report includes data from mass testing Nov-Dec
cwmtafmorgannwg.wales/whole-area-tes…

I think it is with Innova but report does not actually say.

(Note: sens/spec calculations in the report are wrong) Data from Merthyr Tydfil

You can't compute sens and spec directly from this (but the authors did) as only 2.1% of LFT -ves were included compared to 42% of LFT +ves

Correcting for sampling fraction
sensitivity is 17.5%
specificty is 99.7%

Sorry - but there is a dreadful mistake made in computing the sensitivity and specificty of LFT in this report. If you look at Figure 32 (day 1 for example) the estimates of sens and spec are based on a subsample of the study with 364 LFT+ve and 686 LFT -ve. 34.7% are LFT+VE

https://twitter.com/CwmTafMorgannwg/status/1373961796080562186

However, in the whole sample 33,315 LFD tests were completed across 12 centres. Of these, 763 were positive, representing a positivity rate of 2.3%.

Thus the sample used in the test accuracy study is biased to include many more LFT+ves (34.7% compared to 2.3%).

Data on TESTING in SCHOOLS

Results just published to 10th March (;ast Wednesday)
2.8 million tests in secondary school kids, 1324 positives- 0.048% or 1 in 2086. Lowest rate ever observed

Government figures would have predicted around 10,000.
Will post more analysis shortly Using the Government figures from @ab4scambs conservativehome.com/platform/2021/…

Sens=50.1% Spec 99.7% Prevalence of 0.5%
of 2,762,775 tests we would expect 6921 true positives and 825 false positives - nearly 6 times more test positives than have been reported.

Great that @ab4scambs shows some MPs understand the laws of probability (beginning to doubt that there was one) but this justification why we don't need to PCR kids who have positive LFT sadly starts with a fatal flaw

1/8

conservativehome.com/platform/2021/… This is the second time I have tweeted this as one decimal place went for a wander in my first set of tweets. Nothing else changes. Thanks to @d_spiegel for spotting it.

2/8