Coronavirus: Why we don't know how many are being tested

The government has not published the number of people tested for coronavirus since 22 May.

It's also been criticised for not detailing who was swabbed - staff, patients or those isolating at home.

The UK Statistics Authority chairman has written to the Health Secretary Matt Hancock, saying the published official figures are "far from complete and comprehensible".

The Department of Health and Social Care (DHSC) said the publication of headline figures on the number of people tested had "temporarily paused to ensure consistent reporting".

Testing has been a key measure of government performance in handling the outbreak.

Making sure supply could meet demand was one of the five criteria the prime minister said needed to be met before easing lockdown.

And the government acknowledges testing strategically will be vital as lockdown restrictions ease.

But as the programme has expanded, it has become increasingly difficult to interpret and scrutinise the official data.

"People tested" is a helpful separate indicator since the number of tests carried out does not tell you how many individuals have accessed a test. On 22 May, when the data for people was last published, 140,497 tests were carried out on 80,297 people.

Tests vs people

The gap between tests and people tested can be explained by a variety of things.

Some people needed a second swab because their first was not good enough to give a conclusive result. People with "void" or unclear results were sent a new test.

Up to 19 May, 8% of tests carried out at drive-through and pop-up testing sites were inconclusive. The figure for home test kits was not provided.

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There are also good clinical reasons to retest someone - to check whether someone who has previously tested positive is now negative, or to double check a negative result in someone who still has symptoms.

Population surveillance

On top of this, people tested as part of a surveillance study to estimate the level of infection in the population as a whole were counted in the tests, but not the people tested, figures.

The latest round of Office for National Statistics surveillance testing for the period 27 April-10 May involved 10,705 participants.

Together, surveillance swab and antibody testing, which are important but aren't used to diagnose people individually, accounted for almost 30,000 of the just under 130,000 tests carried out on 30 May.

All of these factors mean there are more tests processed than people given a result.

The government has not provided figures on how many individual people received more than one test for each of these reasons, so we can't tell how much each one accounts for the discrepancy between tests and people tested.

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Routine testing

Another possible explanation for the gap is that certain groups of people (like health and care staff, and care home residents) are being tested regularly.

The DHSC was not able to clarify how people who were tested on several different occasions would be counted - as one "person tested" or many.

A spokesperson did refer to a "small percentage of cases where the same person has had more than one test", suggesting routine testing may be limited.

An Imperial College London study, by the same modelling group that has informed much of the government's response, said in April that NHS staff should be tested weekly even if they didn't have symptoms.

This need for routine testing has been echoed by NHS Providers, the body representing hospital trusts.

And Nadra Ahmed, chairwoman of the National Care Association, which represents independent care providers, said routine testing in care homes was "just not happening".

On 28 April Health Secretary Matt Hancock said care home staff and residents could be routinely tested even if they didn't have symptoms.

But Ms Ahmed described this as "smoke and mirrors".

She said she had heard from providers around the country who had requested batches of tests for their staff and residents, and were still waiting 14 days later.

Some hadn't even been able to test their staff and residents once, while others were struggling to get onto the portal.

Home kits

The UK Statistics Authority particularly criticised the inclusion of home kits posted out, but not yet returned, in the number of tests.

Its chairman, Sir David Norgrove, accused the government of using the data to "show the largest possible number of tests, even at the expense of understanding".

Although the DHSC reached its target of providing 100,000 tests a day by the end of April, it has not published data on how many were actually used and returned.

After setting the 100,000 tests a day target, the government moved its focus away from the number of people tested.

In fact, when it came to the "people tested" figures, home kits only showed up in the data once received back for processing in the lab. This may account for some of the gap but, again, we can't say how much.

This in itself appeared to be a source of confusion - even within the department.

Guidance on the website initially said tests done at home or at a pop-up testing centre run by the armed forces did not contribute towards the "people tested" figure. But this note was later taken off the website.

A DHSC spokesperson said these tests were only counted as "people tested" at the point of being analysed in the lab, and that the note was removed "to avoid confusion".

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