From what I've gathered from my searching, the chance to contract HIV from a needle stick in which the needle is contaminated with HIV infected blood (or other secretions) is 1 in 300. My question is about this 1 in 300 number. First, does this 1 in 300 chance include individuals who then begin PEP or is this 1 in 300 number for individuals who were stuck or poked with a needle and did not have PEP? Second, is this 1 in 300 chance usually a direct needle stick? What I mean is that is this 1 in 300 chance usually the result of someone being struck with a needle immediately or very quickly after a needle was used on an HIV infected patient? My reason for asking is I have a phobia of being stuck by, or stepping on a needle when I walk on sidewalks or streets and I want to have an idea of how risky this would be for me. Thank you a lot.

Welcome to the Forum. I'll be glad to try to clarify thing. the 1 in 300 figure reflects the average risk for infection following a single needles stick after than needle has been used on a person with untreated infection.  it presumes that the needle stick has occurred in a setting immediately after the needle was used on the person with HIV.  it does not reflect the reduction in risk for if the person sustaining the needle stick take PEP in recommended fashion.  It also does not reflect he risk of infection if the HIV infected person in whom the needle was used was on effective therapy for their HIV infection. 

Your risk for HIV from an incidental needle stick which might occur if you were accidentally stuck on a sidewalk or while walking barefoot on a beach is far, far lower than the 1 in 300 estimate.  I have never seen a person who acquired HIV from an incidental needles stick.  I hope these comments will help you to address your phobias.  EWH

I appreciate so much your sharing your knowledge. I wanted to be sure I understood you correctly because the language you used in your reply to my first question was a bit confusing to me. 

What I understood you to say was that the 1 in 300 risk associated with a single needle stick is the average risk for an individual stuck with an HIV contaminated needle when the individual sustaining the needle stick DID NOT begin PEP treatment (after the needle stick). 

In other words, the risk for an  individual stuck with an HIV contaminated needle who did NOT then begin PEP is 1 in 300 (and the risk for that individual would be EVEN LESS than 1 in 300 [1 in 1000, 1 in 10,000, or however much PEP reduces risk] if they DID begin PEP after the needle stick). 

You wrote that my chances of being contaminated with HIV were far, far lower than 1 in 300 if I was struck by a needle on a sidewalk, street, beach, etc. Is your far, far lower estimate assuming a needle infected with HIV? 

And finally, regarding my professor and potential blood exposure: I assume that I DO NOT need testing as a result of this situation and can continue having unprotected sex with my girlfriend. Is that correct? 

Thank you for all of your answers and for providing a very useful opportunity for follow up questions.

Pasted your questions, then added my comments aqfterward-

"In other words, the risk for an  individual stuck with an HIV contaminated needle who did NOT then begin PEP is 1 in 300 (and the risk for that individual would be EVEN LESS than 1 in 300 [1 in 1000, 1 in 10,000, or however much PEP reduces risk] if they DID begin PEP after the needle stick)."- CORRECT

"You wrote that my chances of being contaminated with HIV were far, far lower than 1 in 300 if I was struck by a needle on a sidewalk, street, beach, etc. Is your far, far lower estimate assuming a needle infected with HIV?"   Most such needles would not contain HIV.  If they did, and the needle had been used on someone infected with HIV the exposure and time since it was used would act to reduce the likelihood of transmission.

"And finally, regarding my professor and potential blood exposure: I assume that I DO NOT need testing as a result of this situation and can continue having unprotected sex with my girlfriend. Is that correct? "  Absolutely