I was just going to say what about the 3 year old child who got HIV via a blood transfusion.
But, yes, I also think that someone with HIV should tell someone else they have it. Even if not from a legal perspective, it really is the moral thing to do.
Where did this happen? The Red Cross tests donated blood for everything. It anything is afoul, they toss the blood. If you have just a small amount of alcohol in your blood, it gets tossed.
If someone has any contagious diseases, they should abstain from sexual intercourse, in my opinion. That's the moral thing to do.