What is it about this group/hospital that makes you want to be a part of it?

You must assume the interviewer thinks his or her hospital/group is absolutely wonderful...or potentially wonderful with the addition of the right person--hopefully you. You can stroke the corporate ego and begin endearing yourself to the interviewer by invoking the Mission Statement and/or Vision of the hospital or group. Most hospitals will have these, prominently displayed on the landing pages of their websites; they are brief and easy to imbue into your interview strategy. You can tell the interviewer that you find the values you saw in the Mission Statement and/or Vision Statement align with your personal views of how you want to lead your professional life.
Don't actually refer to the Mission Statement and Vision when you answer; just state that you find this group's values align with yours, and you can paraphrase the ones you saw displayed.