From The New York Times:
NEW DELHI — Accepting a just-picked mango from a stranger in Lodi Gardens and then putting it directly into my mouth — skin and all — was stupid. I admit that. But why did my first horrible case of traveler’s diarrhea in India have to result from a mango? I love mangoes, and India’s vast array of deliciously different mango varieties has been one of the great delights of moving here. “You didn’t even wash it?” Dr. Paul Offit, chief of infectious diseases at Children’s Hospital of Philadelphia, asked me later. No. “Even by your standards, that was really stupid,” Dr. Offit said. But what about the local yogurt I had eaten and the probiotic pills I had taken — weren’t my gastrointestinal flora protecting me? Since we all carry 10 times as many bacterial cells as human ones, wasn’t I for all intents and purposes already more Indian than American? “Yogurt probably won’t hurt you, unless it’s contaminated as well,” Dr. Phyllis Kozarsky, an expert on traveler’s health at the Centers for Disease Control and Prevention, said in an interview. But there is no food on the planet that will protect against an onslaught of toxic bacteria, she added.
Despite decades of immunological research and a recent surge of interest in the bacterial garden of the human gut, diarrhea remains the most unpredictable travel-related illness. There is a grim acceptance among Western expatriates and visitors here that they will be felled by it — often on multiple occasions. And there is a host of myths surrounding traveler’s diarrhea, many of which I have cheerfully perpetuated to family and friends. (Well, mostly to my wife.) There are also intriguing mysteries about how natives gain immunity to the food- and waterborne bacteria that prove so toxic to non-natives. I have lived in India for four months, and I have been in gastrointestinal distress five times — roughly once a month. Part of the problem is that Indians are a very hospitable people. Almost everywhere I go, someone offers me food and drink, forcing me to quickly weigh the chance of contamination against the likelihood that a refusal would cause offense.