Fifty-one patients who recovered from coronavirus in South Korea have tested positive again, raising fears the virus can be reactivated.
The patients, from the city of Daegu, South Korea, had all spent time in quarantine while recovering from the virus, but were diagnosed again within days of being released.
South Korea has been among the most successful countries globally in controlling the outbreak, using strict quarantining and widespread testing to slow its spread of the virus.
The number of new cases being diagnosed each day in the country is now at levels last seen as the pandemic was getting underway in February.
The 51 cases were identified as part of a study conducted in Daegu, the epicentre of the outbreak in South Korea, by a team of epidemiologists from the Centers for Disease Control and Prevention.
The center said it did not believe the patients had been reinfected, but that the virus had remained at undetectable levels in their cells and later “reactivated”.
The claim runs contrary to the bulk of current evidence about how the virus works.
Speaking to MailOnline, Paul Hunter, an infectious diseases professor at the University of East Anglia, said: “I agree that these will not be reinfections but I do not think these will be reactivations.
“Personally I think the most likely explanation is that the clearance samples were false negative.”
Coronavirus patients are typically required to test negative twice before being allowed to leave quarantine.
Professor Mark Harris, Head of virology at University of Leeds, said to Daily Mail: ‘The reports that patients who tested negative subsequently tested positive again is clearly of concern.
‘It is unlikely that they would have been reinfected having cleared the virus, as they would most likely have mounted an immune response to the virus that would prevent such reinfection.
‘The other possibility therefore is that they did not in fact clear the infection but remained persistently infected.’
‘It does appear that swabs for the virus are not 100 per cent reliable,’ Professor Hunter said.
Professor Rowland Kao, of the University of Edinburgh, said: ‘It would seem unlikely that this is a common occurrence, and thus should have only a small impact on the overall epidemic projections themselves.’