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.
For, a study has said that one in 10 people may have clinically relevant levels of potentially infectious SARS-CoV-2 past the 10 day quarantine period. The research is published in the international Journal of Infectious Diseases.
Led by the researchers from University of Exeter, the study 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 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 authors believe this new test should be applied in settings where people are vulnerable, to stop the spread of Covid-19.
The paper is entitled ‘Persistence of clinically-relevant levels of SARS-CoV2 envelope gene subgenomic RNAs in non-immunocompromised individuals’.
Professor Lorna Harries, of the University of Exeter Medical School, who oversaw the study said: “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. Furthermore, there was nothing clinically remarkable about these people, which means we wouldn’t be able to predict who they are”.
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.