Posted 10/7/2016 7:29 AM (GMT -5)
He shouldn't get traveler's diarrhea if he takes the necessary precautions. The most important is to not consume any tap water. This includes things like brushing your teeth and ice in drinks. Use bottled water for everything. Don't eat fruit that has a skin (e.g., apple). Make sure meat is fully cooked. Avoid street food. Take packaged food with you that he can eat within his dietary restrictions. His diet on the trip may be boring but that's preferable to having GI issues.
In the last 10 years, I've been abroad ~10 times, including two trips to Asia and several multi-week trips while in an active flare, and I've never had major issues. If he is doing well healthwise, it's important for him to get to do things like this. It helps show that the disease is not in charge.