South Korean health officials say they may have discovered why recovered COVID-19 patients are testing positive for the illness again.
Over the past few weeks there have been multiple reports from South Korea of patients thought to have recovered from the potentially deadly COVID-19 illness testing positive again. As of Wednesday, there were 292 of these "retested-positive" cases, according to the Korea Centers for Disease Control and Prevention (KCDC).
Reuters reported on April 10 that Jeong Eun-kyeong, the director of the KCDC, had said the virus may have "reactivated" rather than the patients becoming infected again, but experts continued to investigate the occurrences.
However, according to multiple South Korean news agencies - including The Korea Herald and Yonhap - it was announced by one of the country's leading virus experts at a Wednesday press conference that tiny traces of inactive virus fragments may be what's behind the positive tests.
"The tests detected the ribonucleic acid (RNA) of the dead virus," Dr Myoung-don Oh, who leads the South Korea's central clinical committee, said, according to The Korea Herald.
Like many countries, South Korea uses the reverse transcription polymerase chain reaction (PCR) testing method, which looks for the presence of the virus' genetic material or RNA. According to the International Atomic Energy Agency (IAEA), which has helped train experts to use the tests, the method is "one of the most accurate laboratory methods for detecting, tracking, and studying the coronavirus".
But the PCR testing method is also very sensitive and Dr Oh said it cannot distinguish between dead or alive virus fragments, therefore leading sometimes to false positives.
Dr Oh said the virus cannot reactivate unless it causes chronic infection, which it does not appear to, unlike some other diseases.
"The COVID-19 virus does not invade inside of the cell nucleus and combine with a patient's DNA… it means that the virus does not create chronic infections," he is cited by Yonhap as saying.
The suggestion that the tests were only false positives caused by inactive fragments lines up with findings from the KCDC on April 26 that "no new case has yet been confirmed that resulted from exposure to the re-positive cases (during the period in which they were re-positives)".
As of Wednesday, South Korea has 10,761 confirmed cases, with 246 deaths.