Very often food poisoning is exacerbated by alcohol. A major part of Tourista is drinking too much alcohol which allows the bacteria or worse to attack the intestinal lining. Drinking makes things worse, it does NOT protect. All the strange fruit, even if you peel it can make things worse also (if you do not trust me, try eating too many mangoes at home, without the extra bacteria even.) There are plenty of ways to pre-treat yourself to lessen the effects of Tourista (check with your doctor). There are also purification tablets that can be used to wash fruit, etc. But better safe than sorry. My husband eats all kinds of things in Mexico that he should not, and has paid dearly with a wide assortment of unintentional souvenirs. Besides just the standard "ridin' the porcelain pony" ailments there are much worse, such as hepatitis and giardia. You will need your liver much more than that tequila with ice or that slice of fresh papaya. Eat and drink only in places you can trust, and NEVER off the street vendors or beach shacks.
Carla (getting down from soapbox-trust me, if you have ever lived with someone with giardia or had it yourself, you don't wanna go there)