April 11 (UPI) -- The World Health Organization said Saturday it's investigating reports that some individuals who have recovered from COVID-19 have been reinfected.
"We are aware of these reports of individuals who have tested negative for COVID-19 using PCR [polymerase chain reaction] testing and then after some days testing positive again," WHO said in a statement to UPI. "We are closely liaising with our clinical experts and working hard to get more information on those individual cases."
Earlier this week South Korea's Centers for Disease Control announced that 91 patients who had tested positive, then cleared as cured after two negative tests 24 hours apart, tested positive again before being discharged from the hospital.
Typically, according to the WHO, it takes about two weeks from the onset of the illness before a patient recovers.
The agency said that more systematic data gathering on recovered patients will be needed before it's possible to draw any conclusions about why some people appear to relapse.
Earlier this week Jeong Eun-kyeong, director-general of the Korean CDC, said the agency will conduct an intensive study of cases of patients who have become re-infected.
South Korea was one of the first countries to see a large-scale COVID-19 outbreak, but its count of cases has fallen continuously since the end of February without extensive lockdowns, largely due to extensive and proactive testing.