Results coming out positive long after recovery
CORONAVIRUS tests are giving people positive results even when they had the virus 70 days ago, a University of Oxford academic has warned, amid fears they are too sensitive.
Prof Carl Heneghan, director of the Centre for Evidence-Based Medicine, said eight days after contracting Covid-19, the chance the infected person will pass the virus on “goes down to zero” if they have no symptoms.
However, he said fragments of the virus could remain in the body for many weeks afterwards – with some studies showing intermittent shedding up to 70 days later – leading to a positive test and skewing the real picture of how many people were at risk of passing on Covid-19.
The warning follows sharp rises in cases across the UK which have led to local lockdowns, despite no increase in hospital admissions, leading to speculation that people are needlessly being told to quarantine. “After about day eight, you can still find the RNA fragments,” Prof Heneghan told the Today programme on BBC Radio 4. “Some studies have reported up to 70 days that you intermittently shed.
“You can understand the importance of this, because what you want to do is find those with active infection and not those with the RNA fragments.”
He said it was “one part of the explanation” why more cases were being identified but hospital admissions were not going up, combined with more young people contracting the virus and not being as badly affected.
“Asymptomatics could have had the infection six to eight weeks ago and are still shedding the virus intermittently, which we can do through faeces and respiratory samples,” he said.
“It’s incredibly important we get highly accurate data so we can understand whether the infection is going up or down. At the moment, what we’re picking up is a lot of noise in the data.” He said the Government needed to take a “much more nuanced approach” to interpreting infection numbers.
Covid-19 is currently diagnosed through a swab test known as PCR. While the test can indicate if a person has the virus present in their body, it cannot say if it is at an infectious stage.
A person shedding a large amount of active virus and one with leftover fragments from an infection that is no longer transmittable would both receive a positive test result. Prof Heneghan said the key was working out what quantity of the virus meant the person was still infectious.
When this cut-off point is established, only those who are carrying sufficient amounts of Covid-19 to make them a transmission risk will be considered positive for the virus.
Meanwhile, those who have fragments of the virus left over from an old infection will not have to quarantine.
Some scientists have warned creating a test which is less sensitive to old virus fragments is a delicate art which could lead to some infectious cases slipping under the radar.
70 Number of days which some scientific studies have suggested people can intermittently shed coronavirus for