It might suck being a white guy from North America if you find yourself with any kind of elevated body temperature while crossing customs, as they are quite manic about pulling people out of the line and quarantining you, and more so on the Chinese border.
You'll see people wearing masks. It's mostly to prevent them from catching the flu, and to help stop the spread of their germs if they have any. It seems like everywhere you go there is an alcohol gel dispenser for you to cleanse your hands with.
So in some ways, you are probably coming to the most prepared place for dealing with flu, as you'll find lots of masks, and sanitization.
I guess if you are concerned about the possibility of catching a flu, then perhaps steer clear of DFK, and do go with any WG that seems lethargic and sick looking. These are both common sense, so I'm not sure why I even typed all that!
Otherwise, carry on, I wouldn't let the flu stop you.
