Dont drink the water, and only eat freshly cooked food. Take insurance which covers you for bandit attacks if at all possible. The Danish football team, having whupped Uruguay 6-1 when Uruguay were top of the South American league, were brought to their knees by swimming in the hotel pool and eating the local food, they had all the food flown in from Denmark from then on, but the damage was done weakened by Montezuma's revenge.