The databases being shared by the U.S. and Canadian Customs and Immigration officials contain a vast amount of personal information – including health related issues.
A Canadian woman was denied entry to the U.S. because of a suicide attempt years earlier. Although officials cannot get into your personal medical records, they do have access to any record that involves law enforcement. In this case, the woman was judged to be a mental health risk and was not allowed to enter until she paid a fee of $250, and her family doctor provided certain medical records. She was also required to sign a form stating she understood the information would be passed to the U.S. government and that she had no control over how it would be used.
See ezbordercrossing.com for more information on what a border official knows about you.