False positive lateral flow tests in children double in a week

The amount of false positive coronavirus lateral flow tests has increased in secondary school children, official data show.

Anecdotal evidence of children receiving a positive lateral flow and then a negative follow-up PCR have circulated on social media and numbers from the UK Health Security Agency indicates the phenomenon is indeed on the rise.

Susan Hopkins, chief medical adviser at the newly-minted UKHSA, has said the body is aware of the trend and is “looking into the cause”.

Figures from Test and Trace, which used to be controlled by the Department of Health and now falls under the remit of the UKHSA, reveal that in the week ending September 22, almost 620,000 students took lateral flow tests at home as part of routine asymptomatic screening and almost 14,000 came back positive.

However, 1,112 (8 per cent) of these pupils returned a negative or void follow-up PCR, indicating the lateral test result was a false positive.

One week later around 580,000 secondary school students took a lateral flow test and almost 16,000 were found to be positive.

Of these tests, 87 per cent (13,863) were later confirmed via PCR, with 13 per cent — or around one in eight — coming back as negative or void.

The reason for the surge in positive lateral flow test results in children remains unknown, with Dr Kit Yates, a Senior Lecturer in Mathematical Biology at the University of Bath, saying it could be down to any one of myriad factors, including faulty lateral flow tests, children manipulating the test to get out of school, or a mathematical quirk brought about by the sheer volume of tests being done.

In an article for The Conversation, the member of Independent Sage explains: “Understanding whether there’s something truly wrong or whether this is just a mathematical artefact has significant ramifications – for testing, contact tracing and the monitoring of the UK’s current Covid situation.

“The UK Health Security Agency’s (UKHSA) chief medical adviser, Susan Hopkins, has noted that the organisation is looking into the issue.

“The UKHSA acknowledges that it doesn’t have an explanation as yet but is investigating because it has “not experienced this before to such a degree”.

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