Greetings.
I would say almost nil. Read this resource (go to misconception of the spread and read about kissing);
http://www.cdc.gov/hiv/resources/factsheets/transmission.htm
Please feel free for your follow up questions.
Dr. Arun
This communication is open till you are satisfied. I have 20 years experience of direct patient care as a surgeon, sports medicine specialist and a medical teacher. Please click accept if I had answered your question. Good feedback/bonus is welcome.