AAAH! Discord mod power abuse!!
@EnderWin If we want to put science to it, it might also be a virus rewriting your cells to be bioluminecent.
We (as humans) are ourself experimenting with adding such genes to beasts, and 'viral therapy' to rewrite people with faulty genes demanding constant treatment just to live, so putting the two together in a wild manner might also be a cause.
As for antibiotics, if it was bacterial, we (again as humans) have made sure that some bacteria already are resistant to all the antibiotics we used to use to kill them, and we know that bacteria can occasionally adopt the immunities other bacteria have gained.
Whether it is bacterial, viral or other, the bioluminecense might also just be a 'marker' added by some science project, who then didn't dare to say anything when their experiment turned out to survive and get past their countermeasures and into the general public. (Or they intentionally infect some people to see what will happen.)
(Although tbh I'd guess it's just an analogy for cancer. So instead of having her lose hair and other gruesome stuff, one can just show some pretty lights and everyone gets it.)