18. No user is entitled to be informed of the existence or be given communication of information concerning him furnished by a third person which is contained in his record, where knowledge of the existence or the communication thereof would make it possible to identify the third person, unless that person has agreed in writing to the disclosure of the information and of its source to the user.
The first paragraph does not apply where the information was furnished by a health or social services professional or by an employee of an institution in the performance of his duties. For the purposes of this paragraph, trainees, including medical residents, shall be regarded as health or social services professionals.