South Korean officials on Friday 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.
some Wuhan residents who had tested positive earlier and then recovered from the disease are testing positive for the virus a second time. Based on data from several quarantine facilities in the city, which house patients for further observation after their discharge from hospitals, about 5%-10% of patients pronounced "recovered" have tested positive again.
Some of those who retested positive appear to be asymptomatic carriers [...]
"In terms of those who retested positive, the official party line is that they have not been proven to be infectious. That is not the same as saying they are not infectious," one of the Wuhan doctors who tested positive twice told NPR. He is now isolated and under medical observation. "If they really are not infectious," the doctor said, "then there would be no need to take them back to the hospitals again."
Obviously (from the quotes above) it's premature to ask what's the real cause of these observations. So, instead I'll ask: have such cases of "reactivation" (positive, negative, then positive tests) been reported in other countries, besides China and South Korea?
According to more recent news from South Korea:
A clinical expert panel on Wednesday [Apr 29] also concluded that recovered coronavirus patients who later test positive for the virus again were not “reactivated” or reinfected, but were false positives.
The head of the committee said the false positives were due to technical limits of polymerase chain reaction (PCR) testing. The country has so far reported 292 such cases.
Still I think the question remains somewhat interesting whether other countries have experienced this kind (false positive) problem to a substantial degree.