If it's so low traffic maybe whenever y'all run into each other you could just do something subtle like a visual cue like a nod or just a "hey how are you?" if they seem to be in a good mood whenever you happen to pass by each other in the workplace.
Not saying you have to be friends with this person but maybe after a few of those small interactions(and a little time) bring it up in a non-direct way...
Best case scenario if he replies to a "hey how are ya?" with "oh good, how about you?" you could casually bring up something like "oohhh, had a patient that came in with (same symptoms as the guy) - we figured out it was this. Don't see that often!"
Hopefully he's drinking at least 50 gallons of water a day, and eating tree bark seems to be a good remedy for GI issues.
Oh wait, is your coworker a human or an elephant?