As you know, epidemiological cohort studies require rigorous approaches, one of which is access to information. In Quebec there's a body I don't know the name of--perhaps Dr. Yang Mao could tell me--but there's a body there that was required to be consulted in terms of release of information.
Also, in Ontario there's a regulation of the...I think the Ontario Medical Act, that we also need to go to so physicians can release patient information. Those two bodies were certainly consulted and agreed to the release, but there definitely was a strong provision for making sure the individuals were anonymous.
Perhaps Dr. Yang Mao, being part of the methodology, might want to add some further answers to that.