By Sam Blanchard Senior Health Reporter For Mailonline
Published: 23:30 BST, 2 September 2020 | Updated: 10:21 BST, 3 September 2020
People still have traces of the coronavirus in their bodies more than a month after they catch it, according to a study.
Because of this, scientists say patients should be retested at least four weeks after first being diagnosed with the illness before being given the all clear.
Research that followed more than 1,100 people in a badly-affected region of Italy discovered that the average time to 'viral clearance' was 31 days.
The scientists said that even if someone appeared to have recovered and didn't have symptoms any more, there was still a strong chance they had the virus - or fragments of it - in their bloodstream and some of them might be infectious.
It has been unclear how long the body takes to get rid of Covid-19 and many people report still suffering for months after their diagnosis, while others only feel ill for a couple of days.
There are also growing concerns that many positive test results being produced in the UK are coming from people who aren't actually contagious or ill but have chunks of the virus still circulating after they have recovered.
Swab tests are the most reliable way of knowing whether someone has Covid-19 because they pick up traces of the coronavirus in the airways, where it causes infection (Pictured: A health worker tests a man in Paris, France)
Researchers at the local health department in Reggio Emilia, northern Italy, looked at the test results from residents in the area.
They considered 1,259 patients who had received a positive test and then a later negative test, showing they had 'received viral clearance' - that is, they were given the all-clear after an earlier diagnosis of Covid-19.
The average time it took to reach this viral clearance was 31 days.
A subset of 1,162 of the patients had been tested at regular intervals after their positive test, with tests done again 15 days after a first positive test, then 14 days after a second positive, then nine days after a third positive.
The strings of tests showed that people continued to carry the virus for weeks after they were first diagnosed.
Among these people, 704 people (60.5%) achieved viral clearance at some point within the 38-day window.
But only 79 per cent of those tested negative a second time, suggesting that a fifth of negative 'all clear' results