Numbers aside, how reliable is Covid-19 testing?

“What we’ve seen very little examination of is the quality and nature of the tests, who is being tested, and how the test result is actually being interpreted and used.” Green peer Natalie Bennett reflects on the government’s ‘Plan to Rebuild’ report released earlier this week and what this means for coronavirus testing.

Natalie Bennett, Baroness of Manor Castle.
Natalie Bennett, Baroness of Manor Castle.

Image: UK Parliament (CC BY 3.0)

Natalie Bennett

A test is fine. But is it a reliable test, and how will you interpret the result?

The government set a target of 100,000 coronavirus tests a day by the end of April – whether for infection of antibodies is unspecified – and since then, reporting and analysis has focused heavily on that single number, whether or not it has been achieved, whether tests have been sent overseas, and other issues around the number.

What we’ve seen very little examination of is the quality and nature of the tests, who is being tested, and how the test result is actually being interpreted and used.

I’m focusing here on the tests for the actual infection, reliable and widely usable antibody tests having many issues.

You will often hear the phrase: “A bad test is worse than no test at all”. But do we have a bad test and bad testing system?

The UK appears to be relying entirely on a diagnostic test that can test for the RNA of the virus itself (polymerase chain reaction test), using a nasopharyngeal swab. 

The government’s Plan to Rebuild released on Monday (11 May) states: ‘…as the government increases the availability and speed of swab testing it will be able to confirm more quickly whether suspected cases showing symptoms have Covid-19 or not. This will reduce the period of self-isolation for those who do not have Covid-19 and their household members.’

The Plan states the new Joint Biosecurity Centre will ‘collect a wide range of data to build a picture of Covid-19 infection rates across the country – from testing, environmental and workplace data to local infrastructure testing (e.g. swab tests).’

The swab test is being described by users in some cases as deeply unpleasant, which may discourage some from testing, or retesting when necessary.

According to multiple accounts, it is also often being self-administered, either through a home test or at a drive-in testing centre, by a potentially ill person (potentially impaired by the illness), and by having to follow complicated and lengthy written instructions.

I have asked the government what is the difference in results between self- and professionally administered tests (UIN HL3853) and what percentage of each are being administered at drive-in centres (UIN HL3589 – answer was due 5 May), but have yet to receive an answer.

Experts have told the media that a significant source of error in tests – particularly false negatives – is likely to come from inadequate sampling. Professor Lawrence Young of Warwick Medical School told the Huffington Post: “The way you take the sample with swabs in the nose and throat is very inaccurate – and indeed, having seen some of this on the TV where people are driving into these testing centres and you see the swabs being taken, I’m very concerned they’re not actually swabbing correctly.” 

Other nations appear to be shifting in the direction of a saliva test, which may produce better samples, and certainly be less unpleasant for the recipient, yet the government’s plan makes no mention of this. 

A Public Health England report revealed ‘discordant results have been identified,’ indicating there have been problems with the tests once the sample reaches the laboratory. Has the testing fully shifted over to the apparently more reliable commercial approach, as the Guardian’s report suggested was happening by the end of April? Yesterday’s announcements did not appear to refer to this.

‘Our Plan to Rebuild’ refers to research on treatment and vaccines, but not to improving or making possible the roll-out of better (more accurate, easy-to-use or faster) tests. 

Independent of the quality of the sampling, testing or conveyance of the results, there is the biological fact that patients are advised to be tested in the first three days of symptoms, as the virus may after that move away from the lungs and deeper into the throat.

NHS England, reflecting these factors said to Pulse Today: “GPs and other NHS staff who have tested negative for Covid-19 should not return to work if they still have symptoms.”

This would appear to conflict with yesterday’s government plan, which says: ‘Anyone with symptoms should isolate immediately, alongside their households, and apply for a test. If a negative test is returned, then isolation is no longer required.’

So there are real questions about how the government sees the results of the tests are to be used.

There is also the issue of timeliness of the availability of the test and the results.The government’s plans states: ‘This cycle of testing and tracing will need to operate quickly for maximum effect, because relative to other diseases (for example SARS) a proportion of Covid-19 sufferers almost certainly become infectious to others before symptoms are displayed; and almost all sufferers are maximally infectious to others as soon as their symptoms begin even if these are initially mild.’

There are multiple media reports of delays current in receipt of test results including from Portsmouth (10 days), Chessington (up to 19 days) and Ipswich (10 days).

In private communication with one member of the public, they told me: “Household of five, three back so far, two still waiting seven days on”. 

And finally, there still appear to be real difficulties in accessing the results, and inefficiency in the use of resources. To give just one example given to me, Bexhill-On-Sea (which has the highest population of elderly residents of any English centre) has a town centre testing station open only to NHS and care workers. Any other resident wishing to be tested has to travel to Brighton (30 miles each way) or Gatwick (50+ miles each way).

So there are major issues that the government needs to answer about its approach to testing, its choice of method and delivery of that method.

This cannot wait for the Baroness Harding’s new Covid-19 Test and Trace Taskforce to get going to be examined.