South Korean officials are concerned after finding more than a dozen coronavirus infections linked to clubgoers in the densely populated Seoul metropolitan area.
The new infections raised fears about another surge in transmissions after the country had eased social distancing measures amid a slowing caseload the past few weeks.
South Korea's Centers for Disease Control and Prevention reported 12 new cases of COVID-19 in the 24 hours before midnight Thursday, the first time in five days the daily jump was more than 10.
Vice Health Minister Kim Gang-lip said the country detected at least 13 more cases in the following hours, all linked to a 29-year-old patient who visited three nightclubs in Seoul's Itaewon district Saturday before testing positive on Wednesday.
Kim said there was a very high possibility more infections will be confirmed as health workers scramble to trace the patient's contacts. He said the clubs' visitor lists show more than 1,500 customers combined on Saturday.
Of the 13 new cases confirmed on Friday, Kim says 12 were clubgoers, including three foreign nationals and one soldier. The other was an office colleague of the patient who was first detected.
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The country has not reported a daily jump above 100 since April 1, which allowed officials to ease social distancing guidelines, schedule the re-opening of schools and allow professional sports to return to action without fans in the stands.