Seoul and nearby Uijeongbu, Gyeonggi Province, were placed on heightened alert for a potential spike in COVID-19 infections, as a string of new virus cases were identified at large hospitals there.

The key concern is Uijeongbu St. Mary’s Hospital, with nearly 2,500 staff members and inpatients, where more than 10 people tied to the hospital tested positive over the course of three days.

The institution, closed until Friday, has been testing the entirety of its staff and patients for the virus. On Wednesday, at least eight more were confirmed to have been infected.

Newly confirmed patients -- a nurse, inpatients and caretakers -- contracted the virus after coming into contact with an 82-year-old inpatient who was diagnosed earlier this week, health officials said.

The patient is believed to have caught the virus through a 75-year-old virus patient who died earlier in the week, about four hours after test results confirmed him positive.

“We are making a concerted effort with Gyeonggi Province and Uijeongbu St. Mary’s Hospital to devise ways to stop the spread of COVID-19,” Uijeongbu Mayor Ahn Byung-young said in an urgent press briefing.

“In preparation for test results to identify potential infections, we are considering using residential treatment centers to house inpatients,” he added.

Amid mounting concerns over front-line medical staff contracting the virus, some 1,800 hospital staff members have been directed to undergo virus testing, health authorities said.

A general inspection is also underway for some 2,500 people tied to the hospital with an aim to narrow down the transmission route.

The number of virus patients in Korea rose by 101 to 9,887, and three more people died, totaling 165 deaths as of Tuesday midnight, according to the Korea Centers for Disease Control and Prevention.

In Seoul, an even bigger hospital -- Asan Medical Center – reported its first confirmed case of COVID-19, potentially linked to the Uijeongbu cluster.

A 9-year-old patient was confirmed with the virus on Tuesday, leading to 43 other inpatients and medics being placed under cohort isolation.

Asan Medical Center is one of the five major hospitals in the capital, equipped with 2,700 hospital beds. The virus patient has a record of visiting the Uijeongbu hospital before being admitted there.

Roughly 500 people linked to the young patient have received virus testing, with all having tested negative.

“We have completed virus testing of high-risk patients, guardians and medical staff, and we will carry out additional inspection,” an official at Asan Medical Center said.

On a daily basis the massive hospital sees an average of some 11,000 outpatients, treats some 2,540 inpatients and some 320 emergency patients, according to the hospital’s website.

Songpa-gu, where Asan Medical Center is located, disclosed online that the 9-year-old patient visited Uijeongbu St. Mary’s Hospital last week due to a headache before going to Asan Medical Center on the 26th.

She initially tested negative for the virus but was retested due to her record of visiting Uijeongbu St. Mary’s Hospital and was confirmed with the virus, according to the district of Songpa-gu.

“For now it is difficult to view the 9-year-old patient as the initial source of infection (at Uijeongbu St. Mary’s Hospital). We need an epidemiological survey to see if her symptoms on March 24th were of COVID-19. We need to look into hospital records and the transmission route, among other things,” said KCDC Director Jeong Eun-kyeong.

By Kim Bo-gyung (lisakim425@heraldcorp.com)