Batman24

Totally out of line. It's not even remotely in question that your privacy was invaded. HIPAA guidelines were broken. We would be fired on the spot had we done this and rightfully so.
You should document this in writing ASAP. If you want to sue you should call a lawyer and let them advise you. If you want to handle this within the company you should file an official complaint with the CEO, HR, the Legal Dept, Risk Management, the head of nursing, etc. Be firm in what you wish to see happen here...additional training, suspension, firing, etc.
Your computer system should be able to record who was in and out of your medical file. This is how they often catch those going through celeb files so chances are whoever did it is caught red handed and it might go behyond 1 or 2 people doing it. They will be mad but I wouldn't give a flying fig. HOW DARE THEY DO THIS. And they do know better. They were nosy and showed a blatant disregard for your privacy. I'd be LIVID.