I had eaten in a shanty restaurant the night before that lacked running water and sanitary facilities. The cook/server kept a baggy over her hands at all times even when going next door to get change. This only served to advise me that she didn't have a clue about sanitary procedures. By the time I was pulling out of Oaxaca, the "tourista" set in. It was truly caused by toxigenic bacteria because it was causing necrosis of the sub mucosal layer of the gut, and the body was expelling it immediately, lest it cause perforation. The abdominal pain and cramping were noteworthy. The diarrhea: not violent, just uncontrollable, and not tolerating any delay. I was traveling north through a very sunny and hot, dry windy desert on the auto pista in open country so, I adapted. I would park the pickup with its nose pointed towards the road, which covered me from behind. I opened the passenger door, behind which I crouched in perfect privacy. The hot desert wind would quickly dry up and blow away what I left behind. I felt that I had paid my dues, and would not now get "tourista" again. Wrong! It took two episodes to get my immunity up to par for Mexico.
My second bout with tourista arose from a breakfast taken at a restaurant just as you approach the autopista tollbooths going north out of Tepic. I was hungry and there were a couple of restaurants that appeared clean by local standards. Not knowing what to eat, I approached a couple of truckers who were just finishing up, and they recommended the food very highly. I chose the green chile, and then went to wash my hands at the sink, the same one the cook would have to use, and found it waterless. The cook appeared highly offended, and told me I would have use the sink in the men's room. It also was waterless. I checked the women's, also waterless. There was no hand-washing going on around that restaurant. The only time the cook's hands would be "cleaned" was when she kneaded the tortilla dough, and then the pathogenic organisms could incubate for hours maybe all day in the warm moist dough. It wasn't bothering the Mexicans, and I still hadn't disabused myself of the idea that I was going to live somewhere deep in Mexico. Besides I had already ordered my breakfast, and I considered myself immune by virtue of my first "tourista dance". When the green chile breakfast arrived it was way too hot in terms of scoville units of capsicum. I can assure you very sincerely, based on that painful personal experience, that too much hot chili pepper and tourista can combine to make a very vicious disease state indeed