Well I've been to Cozumel a few times. Everytime we ate at restaurants on the pier, fat tuesdays and the one across the street waterside. We've also drank the local beer, and of course the frozen thingys (ICE). On excursion, now it's been a year, but I think it was called playa sol? and a paradise island excursion, both times eatinng the local food, ICE, and local beer.
Never had a problem. Imagine what would happen to their economy if a food epidemic broke out on any port or excursion? The cruise ships and all thier $$ would possibly go elsewhere. so I personally consider this a good motivation.
But there really are no guarentees I guess. Just sharing that we've done just fine. Would eat there again if some one would just donate some cruise $$ my way LOL. oh well, have a GREAT time, oh heck you WILL!