Vacationers in poor countries often discuss “traveler’s diarrhea” with the implicit understanding that it has something to do with going places. But it doesn’t – locals get it too, and according to Wikipedia it’s mostly caused by E. Coli. Locals do tend to suffer somewhat less, having built up a lifetime of immunities to the local pathogens, but that doesn’t stop diarrhea from being the third-leading cause of death in the developing world. And it’s not, as commonly thought, that they are just more used to the food. They’re more used to the diseases the food and the water harbor. In its vulgar essence, the diarrhea suffered by people in poor countries is driven by shit getting into people’s drinking water.
That means that the prevention methods espoused by more-sophisticated travelers are often wrong. Almost anything well-cooked is safe, if it’s fresh off the grill; fresh vegetables, commonly rinsed in water, often are not. For most causes of diarrhea in poor countries, meat is not particularly high-risk – but tapwater is.
How do people (especially those who think diarrhea is caused by the local food, or air travel) maintain beliefs that are so far from the truth? I think they’re pushed into them by spotty data. Diarrhea is a random occurrence, with uncertainty in whether you’ll get it, and how long it takes. It also takes significantly longer from infection to onset than people expect: almost all causes take a day or more to hit you. This makes it much harder to figure out what the problem is. So people can come in with some belief, and then always tell themselves a story to justify their belief. “Oh, it must have been that samosa I bought on the street earlier today.” No – you ate a salad, last night.
Considering that, it’s no surprise that it’s hard to get people to improve sanitation practices. Even in places like the US with clean water, people don’t really understand how sanitation works, our friends the tourists being a prime case in point. Not only that, but clean water is a classic public good (your leaky pit toilet affects everyone else in town) so people lack the incentives to invest in it even when they to grasp its value. Indeed, looking at the history of clean water, the changes have almost always come from the top down. I’m convinced the same approach should be applied to the developing world today.