[Herodotus38]

It is primarily through deterrence. Anyone allowed to use an EMR must go through training about HIPAA rules. A waiver is sometimes required that Epic asks you to print out and sign and put in the patient's chart (although they obviously can't prove you did this, it would be an issue if there was a problem later and it turns out you didn't do this, i.e. You would be liable for whatever penalties/prosecution). Furthermore, all usage is recorded and occasionally audited in my system. I'm not 100% sure the auditing is a requirement and true everywhere (definitely with any hospital or large clinic it will be).