The current theory is that my Dad and Josh brought it over with them and spread it around. Dad was the one who had it at the time he flew over, Josh just beforehand. It hasn't seemed to affect anyone from my work nor Danielle's family - just the people who were at the shared apartment and also my Mum, who has had it worse than anyone (not sure if it's the same thing as she has completely lost her voice and is struggling a lot, while everyone at the shared apartment seemed to be suffering from something notably less severe).