Just heard this on CBC radio news while I was out briefly. My impression, having just got back in the car and missed the beginning, was that a number of Canadian patients who had recovered from COVID-19 were testing positive again, but I may have misheard and they were probably talking about this story from South Korea:
At this point no one knows if (a) the virus re-activated but perhaps in a harmless form, or (b) the testing may have been faulty, or (c) something else. But it raises the possibility that getting the disease cannot automatically be assumed to confer immunity. It does for other coronaviruses, but typically only for a limited time. Needless to say, this is being actively investigated and could have serious implications. In any case, it’s no longer just some rumor about a random patient in China.