Just like any traveler from any region of the world risks when traveling to a new destination, your body may encounter a microbe that is unfamiliar and thus reacts to once. Therefore, there is always a chance. To counter this, it is recommended to get Loperamide / Imodium before you travel.
Food in South America is actually as safe as it is at home. And like at home, even after you clean and rinse the ingredients before cooking, there are still some bacteria remaining. Therefore the main difference is that your stomach is familiar with the bacteria at home, and therefore does not react.
In any case, be careful! In the tropics, it is highly recommended to avoid fresh salad, as well as “anything which cannot be peeled or cooked.” In places such as the Amazon, locals do not eat salad. Larger restaurants often provide them because of the demands of tourists. Though, stay away! Choose instead, for example, sautéed Brazilian kale, known as “couve.”It is made with a hint of garlic – another deterrent to the stomach bug!