For now, the most likely explanation of why people are retesting positive seems to be that the test is picking up remnants of the virus.

The KCDC has re-investigated three cases from the same family where patients tested positive after recovering, Kwon says.

In each of these cases, scientists tried to incubate the virus but weren’t able to — that told them there was no live virus present.

Like many countries, South Korea uses a reverse transcription polymerase chain reaction (RT-PCR) to test for the virus. The RT-PCR test works by finding evidence of a virus’s genetic information — or RNA — in a sample taken from the patient.