One in 10 people may still be infectious and can potentially spread the COVID virus even after the 10 day quarantine period, according to new research.

The study, led by the University of Exeter in the UK, used a newly-adapted test which can detect whether the virus was potentially still active. It was applied to samples from 176 people in Exeter who had tested positive on standard PCR tests. The study, published in the International Journal of Infectious Diseases, found that 13 per cent of people still exhibited clinically-relevant levels of virus after 10 days, meaning they could potentially still be infectious.

Some people retained these levels for up to 68 days or more than two months. The team believe this new test should be applied in settings where people are vulnerable, to stop the spread of COVID-19. "While this is a relatively small study, our results suggest that potentially active viruses may sometimes persist beyond a 10 day period, and could pose a potential risk of onward transmission. Furthermore, there was nothing clinically remarkable about these people, which means we wouldn't be able to predict who they are," said Professor Lorna Harries, of the University of Exeter Medical School.

Conventional PCR tests work by testing for the presence of viral fragments. While they can tell if someone has recently had the virus, they cannot detect whether it is still active, and the person is infectious. The test used in the latest study however gives a positive result only when the virus is active and potentially capable of onward transmission.

"In some settings, such as people returning to care homes after illness, people continuing to be infectious after ten days could pose a serious public health risk. We may need to ensure people in those settings have a negative active virus test to ensure people are no longer infectious. We now want to conduct larger trials to investigate this further,a said lead author Merlin Davies, from the varsity.