Back in the early 80's there was a company started I believe in Maryland I can't remember the name but it is very similar to a credit bereau. It was started by some of the largest insurance companies in the US. I haven't heard much about it for a quite a while but when you signed all the paperwork to go to work for a company usually somewhere on it you gave them permission to have your insurance company report to them and to do a check similar to a credit check on you. As most things go it has probably grown in size and I would be sure HIPA rules would be part of it.
In NZ there are some jobs that screen for Hcv but not most. (i.e. arbourers(SP? Tree cutting specialists). If you had Hcv they could not deny your employment because of it but would take precautionary measure re bleeding. Most here do not test.
That doesn't sound legal to me. I think I remember you are in Canada, but still think that sounds like it would have legal implications. Do they not hire people with cancer? I know someone who has Hiv, and he has a job. He writes software, just like me. I think HIPAA protects us here in the states against things like that.