New research has discovered that coronavirus tests may be finding dead traces from weeks-old infections, resulting in false positives that inflate the scale of the pandemic.
The study was carried out by experts from the University of Oxford’s Centre for Evidence-Based Medicine and the University of the West of England. It found there was a risk of “false positives” because of how Covid-19 testing is being conducted.
The scientists discovered that, despite people with Covid-19 being infectious for only around a week, one test used to detect the disease can still give a positive reading weeks after the patient has recovered.
The team examined 25 studies on the widely used polymerase chain reaction test, which is used to determine if someone has the virus in their system. The test takes a sample from a suspected Covid-19 case and uses a process that increases the amount of DNA, or genetic material, in the sample, to enable it to be examined.
The research found that the tests can amplify coronavirus genetic material that is not a viable virus and no longer capable of causing an infection.
Professor Carl Heneghan, one of the authors of the study, said there was a risk that a surge in testing across the UK was increasing the risk of this sample contamination occurring and it may explain why the number of Covid-19 cases is rising but the number of deaths is static.
“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 wrote in The Spectator magazine.
Professor Heneghan said an “international effort” was required to avoid “the dangers of isolating non-infectious people or whole communities”.