I am guessing the nurse might have experienced some mild symptoms and flew back early. Odd someone would leave and return so quickly. Stranger still is that the person left at all considering he/she was being monitored! All it takes is mild diarrhea and we know how toilets flush on airplanes, lots of spray. Yikes
HCW were NOT being monitored. Until the first nurse seroconverted they were not on a list of people under surveillance.
She may have been told to return once the first nurse turned positive.