The discussion should take place in a setting that is private. It should be at a time when you are talking about things in your lives, not when you are getting all hot and heavy on the couch.
It is important that you understand the nature of your disease, how it is spread and how to prevent spreading it to your partner, so that you can communicate that with her.
Talking about sexually transmitted diseases and infections with a partner is a good idea, whether or not you know you have an infection. (Remember, many people have STDs and are not aware of it.) Here are some tips about how to talk about STD testing.