No, they do not have to know that you were even there.. Especially since you are 18, they consider you an adult and your family doesn't have to know a thing.

Thank you, I can pay with money right? They do not need healthcare?

Yes, you can pay cash. Check if you can get a free test somewhere, they may do it for free. You may be able to go through red cross or something. Ask a nurse at school if you're in school.