More than 50 people who recovered after contracting COVID-19 have tested positive again, but the results might have been due to the reactivation of the novel coronavirus, health authorities here said Monday.

The Korea Centers for Disease Control and Prevention (KCDC) said 51 people from Daegu and the surrounding North Gyeongsang Province, the epicenters of the COVID-19 outbreak here, had tested positive for the virus after they were released from quarantine.

KCDC Director-General Jeong Eun-kyeong said the virus was highly likely to have been reactivated, instead of the people being reinfected, as they tested positive again in a relatively short time after being released from quarantine.

The health authorities said a team of investigators has been sent to Daegu to conduct an epidemiological investigation into the cases.

Other virologists and epidemiologists said the positive results from the retesting may have come from the virus reactivating and not from wrong diagnoses.

"There is a pattern of the viral level decreasing and increasing again. An investigation should be thoroughly conducted into whether the level was low enough to show as negative," said Jegal Dong-wook, an infectious disease expert at the Catholic University of Korea.

They also said the COVID-19 virus may remain latent in certain cells in the body and attack the respiratory organs again once reactivated.

"Patients who retested positive are people in which the virus was reactivated or who relapsed," said Kim Tae-kyung, an infectious disease expert at Soonchunhyang University Hospital.

A COVID-19 patient is deemed fully recovered after showing negative results for two tests performed with a 24-hour interval.

The country recorded fewer than 50 new cases of the novel coronavirus Monday, bringing the nation's total infections to 10,284. It marked the lowest daily increase since late February. (Yonhap)