Thread by @andrewleedr

#Masstesting especially of asymptomatic individuals for #COVID19 is NOT a magic bullet solution.

There seems to be a lot of clamour for it but we need to consider not just the utility of testing but also the issues with it.
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A few months back a team of public health researchers @FionaBell19 @lliandme @ScHARRSheffield carried out a rapid evidence review on #masstesting. We found the evidence from around the world to be mixed, patchy and limited.
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NO TEST IS PERFECT. PCR tests for COVID19 can’t always tell if it is current infection or past infection, or whether the individual is still infectious or not. Here's where clinical interpretation and judgment is key.
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Even a high specificity & sensitivity test will give false positives and false negatives, as the predictive power of the tests are influenced heavily by the underlying prevalence of disease.
See Raj Bhopal's piece which articulates well this issue:
sciencedirect.com/science/articl…
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False positives=unnecessary sanctions/lockdown, work for contact tracers, & anxiety for people affected.

False negatives=false reassurance for people who may be infectious!
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J Watson et al wrote a good piece on #COVID19 tests:
No test is 100% accurate... people with covid-19 can be missed by these swab tests. If you have strong symptoms of covid-19, it is safest to self-isolate, even if the swab test does not show covid-19
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bmj.com/content/369/bm…

TEST FOR A PURPOSE!
Tests often need careful clinical interpretation
They are often needed to guide clinical management, inform patient flows in the health and care system, & triage patients. They are also useful as part of communicable disease control & contact tracing.
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There is an OPPORTUNITY COST to mass testing. Someone's got to do it. If you use health staff to swab, what are they not doing instead? Cancer screens, immunisations, maternity checks, diabetes reviews? Mass testing requires resources, is this the best way to use it?
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Feasibility is another issue. Need to consider the end-to-end pathway for testing. How would you collect & process thousands of samples, ensure quality of tests & reporting, whilst protecting data security? How frequently would you need to do the tests? Resources are finite.
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Accessibility & equity of testing is also important. Can tests be accessed by those who need it most rather than the worried well? How would you maintain public trust in the system? People tested may need support & advice esp if + test. Tests should not be "Fire & Forget".
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Good editorial on #covid19 #masstesting in BMJ by @AllysonPollock & others.

bmj.com/content/370/bm…

And good piece on @BBCNewsnight last night by @deb_cohen articulating the issues around #masstesting.