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At least 179 recovered South Korean coronavirus patients have tested positive again for the dangerous bug, officials said.

South Korea’s Centers for Disease Control and Prevention (KCDC) announced Sunday that the tally accounted for 16 new cases detected of patients relapsing from the killer virus, CNN reported.

Patients in their 20s were responsible for the highest number of patients who have retested positive, the agency said.

There were 41 cases (22.9%) of patients in their 20s, followed by 32 cases (17.9%) of patients in their 50s, according to the KCDC.

Jeong Eun-kyeong, director of the KCDC, said that an investigation is underway to determine why the patients were retesting positive.

Jeong has previously suggested that the virus may have been reactivated after remaining dormant in the patients, as opposed to them being reinfected.

South Korea has confirmed more than 10,600 COVID-19 cases, with more than 8,042 patients being cleared of the virus, officials said.