This is because the CDC has found that there is a possibility that the virus might “reactivate” itself even after the patient is seemingly cured. According to the CDC, this was found to be the case with 51 patients who were initially classified as being cured, but later tested positive for the virus again.
This not only means that the patients could get sick again, but there is a chance that they could then spread it once they get home and go back to work or school. According to Jeong Eun-kyeong, director-general of the Korean CDC, “While we are putting more weight on reactivation as the possible cause, we are conducting a comprehensive study on this. There have been many cases when a patient during treatment will test negative one day and positive another.”
It is unclear why this might be the case, but it has been suggested by some the inconsistent testing could be one of the reasons why patients who test negative might test again as positive later on.