I've heard that this has happened to a few people before in extenuating circumstances, but don't know where to search for more information on this. Is there a name for this? What are some major symptoms, and how does it affect the body? How is it identified?
This has never happened (at least to my knowledge), since removing all bacteria from a human being would be extremely difficult and also dangerous. And there is a proven relationship between the human microbiome and stress, but "extenuating circumstances" won't remove all bacteria from your body.
However you can look in the Internet for "germ-free animals", "gnotobiotic animal" or "axenic mice". Caesarean section in aseptic conditions is practiced (a fetus in normal conditions has no germs in it) and the "newborn" is immediately put in a sterilized enviroment. There is plenty of research with this kind of animals.
I hope my answer was useful for you! Cheers!