Leading researchers warned almost two months ago that the test for COVID-19 used by the NHS and Public Health England was “significantly less sensitive” than other commercial tests.
The research found a “lower rate of detection” in the UK test – especially in people with rare lung conditions – warning that this lower performance could help “propagate the epidemic”.
The government is already under pressure to explain why the UK has continued to use COVID-19 tests known to be less reliable than commercial alternatives – while infection and death rates have surged.
This week openDemocracy published leaked internal documents showing that, due to “discordant results”, all NHS and Public Health England labs were ordered to urgently switch to commercially available testing kits by 23 April. That deadline has now been missed.
A leading pathologist told openDemocracy that the NHS test’s lesser sensitivity meant it would “miss 25%” of positive results. Public Health England disputes this figure, claiming that its test produced “different results to alternative tests in less than 2% of samples”.
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However, researchers have pointed out that failure to detect 2% of positive cases in 100 people, assuming ninety are not infected, amounts to an average of 20% of positive cases being missed.
Public Health England has repeatedly declined to specify what it deems to be an acceptable rate of failure on COVID-19 tests, stating only that “no diagnostic is 100% sensitive”, and that its transition to alternative tests is almost complete.
Health secretary Matt Hancock, who has repeatedly said that “no test is better than a bad test”, is also facing fresh criticism today over failures in the roll-out of testing for key workers.
Hancock has vowed that the UK will be carrying out 100,000 tests a day by the end of April – a target which is now widely also expected to be missed.
Hong Kong research warning
The research indicating a “lower rate of detection” in the NHS test was carried out by a team from the University of Hong Kong and its allied hospitals. It was published in early March by the US-based Journal of Clinical Microbiology, regarded as a high-impact science publication.
In the research paper the test developed by the Hong Kong team is compared to the UK’s CoV-2 test, or the ‘P2’ test as it called in the paper. This P2 test was initially used in thirty laboratories throughout Europe.
In the paper, the P2 test is repeatedly described as “less sensitive”, performing less well in detecting COVID-19. One passage describes it as unable to detect “positive specimens” that were detected by the Hong Kong team’s own test.
Tim McHugh, head of the Centre of Clinical Microbiology at the Royal Free Hospital in London, told openDemocracy that there were broad similarities between the Hong Kong test and those now commercially available.
Responding to questions from openDemocracy about the lower sensitivity and detection rates of the UK test, Public Health England has not challenged the Hong Kong research.
But Sharon Peacock, director of the National Infection Service at Public Health England, defended the UK’s testing regime.
She said: “Method developments for tests are commonly published in academic journals and would still need to be independently assessed before adoption. This process takes several weeks.”
She added: “Rapid migration to commercial kits was always the intended strategy for expanding capacity following the emergency development of a first-generation test. By the time this [Hong Kong] paper was published, work was already under way to move to commercial tests and the first was introduced within days.”
25% of ‘missed positives’
While Peacock did not explain why a test known to be less sensitive in detecting COVID-19 is still in use in UK labs, she said: “Following rigorous evaluation we learned that the PCR test [P2] produced different results to alternative tests in less than 2% of samples and we issued immediate actions to laboratory staff to ensure the continued reliability of the test.”
And she described the figure, supplied by a leading pathologist, of “25 missed positives” in Public Health England tests as inaccurate.
However the team of researchers who provided the 25% figure to openDemocracy described the statement by PHE as a “sleight of hand”.
One said: “The principle is this: if you look at 100 samples and ninety of them are negative then ten will be positive. However if your test only picks up eight of the ten as positive, then you are missing 2% of the total.
“That might appear not too bad, but if you look at the ten positives, you have missed finding two of the ten – you have missed 20%. That is serious.”
Criticising how Public Health England operates, he added: “Public Health England is a citadel, difficult to break through. They have a command-and-control mentality that makes it difficult for them to react to changes once they have taken a decision. That is what is happening here – only this time, the consequences are potentially catastrophic.”
Another leading microbiologist said: “We offered our own test numerous times to PHE. And every time our offer was ignored.”
“Quality assurance difficulties”
The advice from the National Infection Service in the leaked directive seen by openDemocracy, dated 11 April, said there was evidence the NHS test (or “CoV-2 assay”) suffered from “quality assurance difficulties” and that “some discordant results” had been identified.
The memo identified a “shortage of swabs” and the specialist fluid used to “transport” material to the testing labs as causing variations in the performance of the CoV-2 test.
After openDemocracy reported on flaws with the CoV-2 test, health minister Helen Whately told Sky News that some of the UK’s COVID-19 tests were “not up to scratch” and that retesting had been taking place.
The Department of Health and Social Care subsequently told openDemocracy that only “two labs” were involved and this had “impacted fewer than 2% of samples”.
openDemocracy has asked the department to specify which labs were involved, and the total scale of testing. At the time of publication, it had not offered any numbers that could be checked.
Tim McHugh at the Royal Free Hospital, commenting on the overall testing regime in the UK, told openDemocracy that normally test developments “often take more than a year, yet all of this has been pushed into a matter of months”.
He acknowledged that the issue is “political as well as clinical”.
Public Health England has told openDemocracy the “vast majority of NHS trusts are already using commercial kits and others will be transitioning to such kits in the coming weeks.” The spokeswoman said it was not PHE’s role to direct NHS labs on what they should do.