Why did David's servants get the King a young virgin, to keep him warm on his death bed?

I know it seems strange because they did things so differently in those days. They got a virgin in order to make sure no one would have a venereal disease. In those days they had no way to test it except to know whether they are a virgin or not. That's one view point at least. They wanted him to be able to have sex if he felt like it. It was just a matter of safety so there would be no doubt. His wives had been defiled by his rebellious son, Absalom, who was trying to take over the kingdom.