South Korean officials yesterday reported 91 patients thought cleared of the new coronavirus had tested positive again.
Jeong Eun-kyeong, director of the Korea Centers for Disease Control and Prevention (KCDC), told a briefing that the virus may have been "reactivated" rather than the patients being re-infected.
South Korean health officials said it remains unclear what is behind the trend, with epidemiological investigations still under way.
The prospect of people being re-infected with the virus is of international concern, as many countries are hoping that infected populations will develop sufficient immunity to prevent a resurgence of the pandemic.
"The number will only increase, 91 is just the beginning now," said Kim Woo-joo, professor of infectious diseases at Korea University Guro Hospital.
South Korea on Friday reported 27 new cases, its lowest after daily cases peaked at more than 900 in late February, according to KCDC, adding the total stood at 10,450 cases. The death toll rose by seven to 211, it said.
Wuhan to keep testing residents
Meanwhile, China's Wuhan city, where the global coronavirus pandemic began, is still testing residents regularly despite relaxing its tough two-month lockdown, with the country wary of a rebound in cases even as it sets its sights on normalising the economy.
The country reported 42 new cases on Thursday, down from 63 a day earlier. Of the daily total, 38 were imported, down from 61 on Wednesday.