One in ten people may still be infectious for SARS-CoV-2, the virus that causes Covid-19, after the 10 day quarantine period, according to a study.
The research, published recently in the International Journal of Infectious Diseases, used a newly adapted test which can detect whether the virus was potentially still active.
The test was applied to samples from 176 people in Exeter, UK, who had tested positive on standard PCR tests.
The team led by researchers at the University of Exeter 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, the researchers found.
They 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 virus may sometimes persist beyond a 10 day period, and could pose a potential risk of onward transmission," said Professor Lorna Harries, of the University of Exeter Medical School, who oversaw the study.
"Furthermore, there was nothing clinically remarkable about these people, which means we wouldn't be able to predict who they are," Harries said.
Conventional PCR tests work by testing for the presence of viral fragments.
While these tests can tell if someone has recently had the virus, they cannot detect whether it is still active, and the person is infectious.
However, the test used in the latest study 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," said study lead author Merlin Davies, of the University of Exeter Medical School.
"We may need to ensure people in those setting have a negative active virus test to ensure people are no longer infectious," Davies added.
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