Health authorities say that one out of four COVID-19 cases reported in the past two weeks had an unknown transmission source.

According to the Korea Disease Control and Prevention Agency(KDCA) on Tuesday, the routes of infection for 25 percent of two-thousand-209 new cases reported in the past two weeks remain unknown. That rate is the highest to be posted since April when quarantine authorities began to compile related data.  

The percentage of COVID-19 cases with unknown routes began to surge last month following a spike in infections in the greater Seoul area. Since August 30, the percentage has topped 20 percent.  

Though the jump in infections is showing signs of slowing down, the percentage of cases with unknown routes is likely to remain around 20 percent for the time being.