So far as I am aware, it's used in many countries. It's used in cases where you have undergone some sort of serious treatment which kills all the normal bacterial in your digestive system. If you just let the bacterial grow back randomly, you run the risk of dangerous bacteria happening to get a head start by chance and taking over before the normal benign bacterial can get a foothold. So what they do is to insert some bacteria from a healthy person to give the "right sort" of bacteria a head start. It's also used to treat certain chronic gut diseases which are caused by the "wrong" sort of bacterial having taken over.
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