Very small amounts of the HIV virus have been found in saliva (spit) of infected people but as far as we know contact with saliva has NOT passed HIV/AIDS before. Open mouth kissing is extremely low risk for passing HIV but if either partner has sores/cuts in or around the mouth, or even the upper gastrointestinal tract, it is possible for the virus to pass this way. Dental jobs also put you at increased risk of infection.
Attribution: Straight Talk Foundation