With a few simple precautions, traveler's diarrhea should not pose a worry.
This appeared, in edited version, in my March '00 "Ask RSD" column in Rodale's Scuba Diving:
"1. "Do I need to worry about "La Turista"/"Montezuma's Revenge" in Cozumel?" Rich T., Clark, NJ.
Most travelers to Coz report no problem with diarrhea. If concerned, the first step is watching what you drink. Major hotels and restaurants use purified tap water and ice--if in doubt, ask. Many supply bottled water free, and it can be purchased almost anywhere--domestics are the best buy. For extra care, brush teeth/rinse toothbrushes with it. Bottled beverages are generally very safe, but avoid unpasteurized products. Lime or alcoholic spirits may make drinks tastier and more fun, but don't count on them for protection.
Watch what you eat: (1) avoid or work your way up to greasy, fatty and spicy foods, and items you are not used to; (2) eat only fruits and vegetables which have been peeled/ thoroughly washed, and best to stick with the well cooked; (3) things like steak tartare, ceviche and raw shellfish can be inviting trouble; and (4) pass on street vendors and places that appear unhygienic.
Many physicians caution individuals against taking antibiotics preventively without a sound reason. If your diarrhea is caused by something other than a microorganism, or by one which is not targeted by or resistant to the antibiotic being taken, the drug simply make things worse. Antibiotics used to prevent and treat some types of diarrhea include Septra, Bactrim, Vibramycin, and Cipro. These are not medications to be used without physician consultation, even if some can be purchased in Mexico without a prescription. They can cause a severe or fatal allergic reaction, and some can cause sensitivity to the sun, sometimes extreme; special precautions need to be taken when using them. Starting Pepto-Bismol several days before and throughout the trip can be helpful, although this compound may not be well tolerated by some (e.g., those who do not tolerate aspirin), should not used with certain other drugs, and is not intended for long term use.
If you are stricken, some experts recommend seeking medical attention if diarrhea last more than two days, or is accompanied by fever, headache or bloody stool. Pepto-Bismol is also used for the treatment of diarrhea, although under a more aggressive regimen. Along with the antibiotics mentioned above, other medications given for the control of symptoms include the prescription drug, Lomotil (prescription only in the US), and the over the counter product, Imodium, although they can cause complications in those with serious infections, and may even prolong the course of the illness while controlling some of the features. Prescription antidiarrheals are also not to be used without physician consultation.
Diarrhea by its very nature results in fluid loss, drugs like Lomotil and Imodium can be drying, and many manufacturers recommend that water be taken liberally while on antibiotics. If you get ill, drink plenty of water & sports drinks, even more if taking medication.
There is no reason to fear diarrhea on Coz given common sense measures. If you take any medications, understand their adverse effects and carefully follow directions. Should you be stricken on Coz, there is a clinic well versed in treating the disorder--your hotel can direct you."
As regards raw salads, the nature of many vegetable leaves, like lettuce, render them difficult to thoroughly clean. As such, you may want to give them a pass.
Hopefully you found this informative.
DocVikingo