Did you say ghost? Because if you did I can think of any number of ways. As a member of the International Thriller Writers (means nothing; all you have to do is be admitted and pay the meagre dues...) with, now, seven books under my wing (none of them selling, BTW) I think about such things all the time but REFUSE to write the standard kill-em-off.
First, it depends upon how you intend to define “ghost” because it makes no diff, otherwise, where the “person” comes from if, by ghost, you mean an actual force of energy released from its earthly matter. In that event, the “ghost” could have knowledge of virtually EVERYTHING, almost like a god, and could make use of whatever is in the medical facility. And manipulate it in virtually any fashion.
If you want to restrict the “ghost” to some mundane creature that has been traditionally subsumed by human hands or natural causes and captured in an interdimensional world—naturally bound in some fashion to his or her native culture despite being located elsewhere—then you still have the alternative of giving this creature supernatural “senses” if not “powers.” Namely, the ability to “sense” foreign substances previously unknown to him or her in life and their capabilities, i.e., their ability to poison people without being detected, even from a distance. Being able to ascertain through a voodoo-like magic which combination of substances to use and via mind-control convince people to do that combining for them.
But then it is a question of “where” the ghost is located. In Africa or in this clinic. In this clinic? Much easier all around. Simple swap and mop job. And then, do you want him/her to get away with it?