Authorities recently discovered a disturbing trend.  

Some patients who had already recovered from the coronavirus, later tested positive again. South Korea has reported over 350 cases like this, while five to 15 percent of recovered patients here in China fall into this category. 

What's really going on? Are these patients actually getting infected again? 

First things first, "retesting" positive doesn't necessarily mean that these recovered patients were infected again. There could be traces of the virus leftover inside the patient's body or just an inaccurate test result.

Reason No. 1: Virus fragments remained in the patient's body. Recent data has shown that patients expel leftover materials from their lungs during the recovery phase, and these dead cells can produce positive test results.

This is part of the healing process, but doesn't mean these patients have been reinfected.

Reason No. 2: Inaccurate test results. There are a number of reasons why this could happen, including issues with the chemicals used in the test, and the way the sample was collected and stored.

For example, one of the most common tests is swabbing a patient's throat. Samples are taken from the upper respiratory tract. But the virus could be hiding in the patient's lower airways, and that could cause a false result.

Are these patients infectious then?

Unfortunately, there's still no concrete answer in the studies to date, but experts from both China and South Korea say there is an "extremely low risk" for these patients to infect others. 

(Video produced by Wang Zeyu; filmed by Fu Gaoliang; edited by Zhao Yuxiang)