The tests used to find out if someone is COVID positive could be finding traces of the virus that are no longer active, some scientists are saying.
A study by members of the University of Oxford’s Centre for Evidence-based Medicine (CEBM) and the University of the West of England found that there was a risk of “false positives” because of the way people are currently tested for coronavirus.
They looked at 25 studies on the polymerase chain reaction (PCR) test – the very sensitive test widely used to find out if someone has the virus in their system.
The test gives a positive or negative result, which the scientists say amounts to a simplistic “yes” – someone has the virus, or “no” – they don’t have the virus.
But they found the tests were able to detect traces of the virus’s genetic material for a much longer period than it remains infectious – meaning a person who tests positive may have the virus in their system, but won’t necessarily pass it on.
Other genetic material it detects might be fragments of dead virus – which have already been dealt with by a body’s immune system.
One of the study’s authors, the CEBM’s Professor Carl Heneghan, told The Spectator magazine there were also issues with the way the tests check for the virus and there was a risk that a surge in testing across the UK was increasing the risk of contamination.
He said it may be part of the reason why the number of cases in the UK is rising but the number of deaths from COVID-19 is remaining static.
Prof Heneghan wrote in the magazine: “Evidence is mounting that a good proportion of ‘new’ mild cases and people re-testing positives after quarantine or discharge from hospital are not infectious, but are simply clearing harmless virus particles which their immune system has efficiently dealt with.”
He said an “international effort” was needed to avoid “the dangers of isolating non-infectious people or whole communities”.
The authors wrote in their conclusion of the paper, which was published as a pre-print on the Medrxiv online journal and is yet to be peer-reviewed: “Prospective routine testing of reference and culture specimens are necessary for each country involved in the pandemic to establish the usefulness and reliability of (the) PCR (test) for COVID-19 and its relation to patients’ factors.
“Infectivity is related to the date of onset of symptoms and cycle threshold level.”
PCR tests work by taking a sample from a person and applying a process to increase the amount of DNA or genetic material in that sample, so that it can be examined.
The experts say there is a risk the tests can amplify COVID-19 genetic material which is not a whole virus, or material which is no longer capable of causing a full-blown infection.