South Korea, on Tuesday, tested 277 recovered coronavirus patients as positive for COVID-19. They were retested positive, according to the Korea Centers for Disease Control and Prevention (KCDC). Experts said that it was due to inactivated traces of virus fragments in the body.

South Korean health experts said on Wednesday that recovered coronavirus patients may have tested positive again due to traces of virus fragments that have been inactivated. The country's central clinical committee for emerging disease control said that there was no presence of the live virus in such cases, while they refuted the theories that say, the virus reactivates and re-infects, reported Yonhap News.

The expert committee further said that the patients retested positive because 'fragments of the virus' had remained in their bodies which showed up in tests. The test used is reverse transcription-polymerase chain reaction (PCR test) to detect the novel coronavirus. It tests for the infection by finding the genetic information or RNA of the SARS-CoV-2, from the samples taken.

PCR test is very sensitive

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The PCR test proves to be so sensitive, said the experts that it could still pick a small amount of viral RNA from cells even from those who recovered from COVID-19.

"RNA fragments still can exist in a cell even if the virus is inactivated," said the experts in a press release. The case was more likely that retesting positive meant that the test picked up virus RNA that's already been inactivated, they added.

Reactivation of coronavirus virtually impossible

The committee said that it was 'virtually impossible' for the novel coronavirus to reactivate unless the pathogen causes 'chronic infections.' Oh Myoung-don who heads the committee further said that the cases where people were retested positive were due to technical limitations of the PCR tests. The coronavirus doesn't "invade inside of the cell nucleus and combine with a patient's DNA," said Myoung-don, meaning that it does not create a chronic infection.

He cited HIV and hepatitis-B virus as different from SARS-CoV-2 virus as the former stayed dormant inside the cell nucleus causing chronic infection. Acute illness develop suddenly and last for short times but chronic ones develop slowly and take years to clear or may remain throughout life. There are concerns about whether COVID-19 is chronic as many stayed for a longer time in the hospital to get cured.