The HIPAA Privacy Rule explicitly excludes from the business associate requirements disclosures by a covered entity to a health care provider for treatment purposes. See 45 CFR 164.502(e)(1).
Therefore, any covered health care provider (or other covered entity) may share protected health information with a health care provider for treatment purposes without a business associate contract. However, this exception does not preclude one health care provider from establishing a business associate relationship with another health care provider for some other purpose.
For example, a hospital may enlist the services of another health care provider to assist in the hospital’s training of medical students. In this case, a business associate contract would be required before the hospital could allow the health care provider access to patient health information.