South Korea reported more than 100 new COVID-19 cases for the second consecutive day Thursday, due to sporadic clusters of infections across the country, keeping health authorities on edge ahead of the Chuseok holiday.

Korea added 125 more COVID-19 cases -- 109 locally transmitted and 16 imported -- in the 24 hours ending Wednesday at midnight, pushing up the total caseload to 23,341, according to the Korea Disease Control and Prevention Agency.

Korea saw fewer than 100 new cases for three straight days beginning Sunday, after which the daily tally bounced back. Before that, the country reported triple-digit gains in numbers of new cases for 37 days in a row dating to Aug. 14. The number peaked at 441 on Aug. 27.

Clusters of infections continue to pop up largely in the Seoul metropolitan area, home to nearly half of the country’s population, hampering the government’s efforts to bring the virus situation stably under control before Chuseok. During the holiday, which runs from Sept. 30 to Oct. 4, millions of people are expected to travel across the country.

A new cluster of infections was reported at a day care center in western Seoul, with 13 people confirmed to be infected.

At a care home for patients suffering from mental illness, 10 more people tested positive for the coronavirus, raising the total number of cases linked to the facility to 38. Among them, 30 patients were on the same floor. Seven of the 10 newly diagnosed people had no symptoms.

A total of 58 people tested positive for the coronavirus from Severance Hospital, one of the country’s biggest general hospitals, as of Thursday, up eight from Tuesday. Some 43 people and 20 people tested positive from an office building and a public sauna in Seoul, respectively.

Health authorities are struggling with contact-tracing, with sources of infection for 24.7 percent of the new cases reported Sept. 11-24 remaining unknown. This could mean the virus is spreading undetected in local communities and there could be an explosive spike in infections at any time. 

To prevent a resurgence of COVID-19 after the Chuseok holiday, the government is to lay out detailed virus control measures Friday for the period from Sept. 28 to Oct. 11, which has been designated a special quarantine period.

Of Thursday’s locally transmitted cases, the vast majority were in Greater Seoul -- 39 in Seoul, 10 in neighboring Incheon and 43 in Gyeonggi Province, which surrounds the capital. Outside the Seoul area, cases were reported from all administrative cities and provinces except for Gwangju, Ulsan, Sejong, South Jeolla Province and Jeju Island.

Of the 16 imported cases, 11 were identified while the individuals were under mandatory self-quarantine in Korea, with the other five detected during the quarantine screening process at the border. Ten came from Asia, three from Turkey and three from the United States. Twelve of these imported cases involved foreign nationals.

Of the 10 people from Asia, six were from Uzbekistan, with five of them being Uzbek nationals.

The government said Thursday that it had decided not to recognize negative COVID-19 results issued by two of three Uzbek medical institutions, taking issue with the credibility of test results. Two other Uzbek institutions instead will be designated.

Uzbekistan has been listed as one of six high-risk countries by the Korean government, which requires all arrivals from the country to submit negative COVID-19 test results issued within 48 hours of the traveler’s departure.

So far, 52 out of 421 people who arrived from Uzbekistan have tested positive in Korea after they turned in negative results upon arrival issued by Uzbek medical institutions, according to the KCDA.

The number of cases imported from Uzbekistan was six on Thursday, three on Wednesday and two on Tuesday. As of Thursday, five more people had died from the virus, bringing the death toll to 393. The overall fatality rate stands at 1.68 percent.

The number of COVID-19 patients in serious or critical condition was 126.

So far, of the 23,341 people confirmed to have contracted the new coronavirus here, 20,832 people have been released from quarantine upon making full recoveries, up 182 from a day earlier. Some 2,116 people are receiving medical treatment while under quarantine.

The country carried out 12,100 tests in the past day, with a total of 2,268,999 tests done since Jan. 3. Some 20,782 people were awaiting results as of Thursday.

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