South Korea reported 153 new cases of COVID-19 on Thursday, a slight jump after three days of around 100.
Of which, 145 were local infections and more than 80 percent were from the densely populated capital region.
Over the past two weeks, cases with untraceable sources of infection surpassed the 25 percent mark, the highest it has ever been.
Public health officials have been trying to figure out why and on Thursday, found its first 'silent spreader.'
Since June, Seoul city government has been receiving applications from citizens wishing to take free pre-emptive coronavirus testseven if they haven't come into contact with a COVID-19-confirmed patient.
After testing more than 85-hundred people, Seoul city found one person to be COVID-19 positive.
This patient is now in quarantine and receiving care according to guidelines.
Authorities say this rare find helped them realize the importance of conducting pre-emptive tests.
Further checks are to be carried out on over 25-thousand people working at medical facilities.
With the virus having infected more than 30-million worldwide, public health authorities admitted during Thursday's briefing that COVID-19 is not easy to contain.
"Governments are trying to contain the spread by strengthening quarantine measures, but with COVID-19 being extremely contagious, the disease has been consistently difficult to contain."
Public health authorities continue to underline the importance of wearing face masks.
"I stress once again that without a vaccine or a cure, masks are the vaccine and a safety belt that prevents you getting infected or infecting others."
Health authorities also worry that the virus' spread could be exacerbated further with people in South Korea expected to travel during the upcoming Chuseok holiday.
Kim Yeon-seung, Arirang News