A prison officer working at a detention center just outside of Seoul tested positive for COVID-19, authorities said Friday, triggering concerns that the prison could become a new cluster of infections.

A 28-year-old man, who works at the Seoul Detention Center in Uiwang, Gyeonggi Province, tested positive for COVID-19 Thursday. He neither visited bars and clubs in Itaewon nor contacted anyone who had been to the party district in Seoul.

The officer was found to have been infected through a friend who visited clubs in Itaewon when their paths crossed -- in what is believed to be a tertiary transmission case linked to the Itaewon outbreak.

The prison officer attended a wedding with the friend, who visited the same karaoke room in northern Seoul in the same time frame as a confirmed patient. The patient tested positive after coming into contact with another confirmed patient who had visited nightclubs in Itaewon.

The prison officer exposed the virus to some 277 detainees and prison employees for about four days after he came into contact with the confirmed patient. Six other officials who were in close contact with the infected officer have all tested negative.

Officials at the detention center immediately disinfected the venue and are under self-quarantine 23 other employees and 254 inmates, according to the Justice Ministry.

Cho Ju-bin, who is under arrest on suspicions he blackmailed girls into sharing sexual videos in mobile chat rooms, is among those who have been exposed to the virus by the infected officer.

Former President Park Geun-hye has also been serving her term there since she was arrested in March in 2017 over corruption charges.

The prison officer’s infection put the judiciary and the prosecution on alert.

As a precautionary measure, the Seoul Central District Prosecutors’ Office also suspended grilling sessions scheduled for Friday. Some 34 employees, who came into contact with seven inmates, were ordered to self-isolate.

Non-urgent trials scheduled for Friday at the Seoul Central District Court and Seoul High Court were suspended and the buildings were disinfected. The trials are to resume on Monday.

As of Friday noon, a total of 153 have been reported in connection with the Itaewon cluster, with secondary and tertiary transmissions underway across the country, according to the Korea Centers for Disease Control and Prevention.

Korea reported 27 new cases on Friday, bringing the country’s total infections to 11,018, according to the KCDC.

By Ock Hyun-ju (laeticia.ock@heraldcorp.com)