A health care provider does not need your permission to share your medical information for treatment purposes within an HIE, just as a doctor does not need permission to send your records via fax to another doctor for treatment purposes. This is true even if your health record is going to a doctor you have never met before. The idea is that this information is shared only when necessary and only for treatment purposes. However, some HIEs, recognizing that HIEs involve many more patients and new methods of sharing, do give patients the ability to opt out of the HIE.
Taken from the video series at World Privacy Forum.