Where did you hear about people getting sick? And what is the reason? And how sick? And, do your guests travel a lot? We have been to several all-inclusives in Mexico, and have always heard about people getting sick... yet we have not. Please keep in mind that anytime someone travels, sleeps differently, changes eating patterns, climate, is in the sun a lot, and has a lot of alcohol, there is going to be some physical consequences. If this is what you have heard, I would be upfront about it with your guests; recommend immodium and other such things, that they drinks lots of (bottled) water, and go easy on the unusual foods, at least for the first few days.