My friend cut himself with a knife we were using to cut a cheesecake. I used the knife immediately after to cut myself a piece, which I ate right away. I bite my lips and the inside of my mouth a lot. Assuming that I have an open wound in my mouth and assuming that he is HIV positive, what is my risk of infection?
Thank you for your inquiry. From what we gather from the question, you were asking about the risk of acquring HIV after cutting(and eating) a piece of cake with a knife with which your friend had just cut their hand. From the information given, this scenario is determined to be No Risk (transmission of HIV is not possible in the given scenario).
When assessing the risk of HIV transmission, we focus on the activities involved and not the persons involved in said activities. Speculating on an individual's HIV status does not provide reliable information when assessing risk of HIV transmission. The activities engaged in, however, provide us with the opportunity to provide an evidence based risk assessment.
The scenario mentioned above does not meet the three components of the transmission equation(1). It does not satisfy the equation because:
For HIV transmission to occur, the 3 components of the transmission equation(1) must be met. There must be a bodily fluid containing HIV(ex: blood, vaginal fluids, breast milk, anal secretions, semen), direct access to the blood stream(ex: inside the vagina or anus, mucosal membranes), combined with a risky activity(ex: unprotected vaginal/anal intercourse, mother-to-child, sharing needles).
Saliva contains enzymes that inhibit the transmission of HIV(2).
HIV does not survive long outside the human body (such as on surfaces), and it cannot reproduce outside a human host(3).
The scenario you provided has been assessed as No Risk. You state that your friend cut their hand with a knife, and shortly after you used that same knife to cut and eat a piece of cake. You say that you bite your lips and the inside of your mouth often and want to assume that there are wounds inside of your mouth. From above, we know that HIV does not survive long outside the human body (such as on surfaces like a knife), and it cannot reproduce outside a human host(3). This means that any blood on the knife had been outside of the human host, exposed to environmental conditions, and thus unable to reproduce. There also must be direct access for a bodily fluid containing HIV to enter the bloodstream. The cuts in your mouth that you have described can be considered superficial cuts. Superficial cuts are not deep enough to provide direct assess to the bloodstream. The cuts would have to be very deep and actively bleeding to provide direct access to the bloodstream. All that being said, saliva contains enzymes that inhibit the transmission of HIV, another reason why the scenario described has been assessed as No Risk.
Recommendation: No need for HIV test with the scenario provided, refer to a physician for other health related questions.
Regards, AIDS Vancouver Helpline/Online, Hilary