Q: ICU resident had needle stick while performing a procedure in an HIV positive patient. Resident decided not to take post-exposure prophylaxis. What are her or his chances to contract HIV?
 

Answer: The average risk of seroconversion after a needle stick injury is about 3 per 1000 with no prophylaxis.  To be precise, it is between 0.23 to 0.36 percent.

 References: 

Tokars JI, Marcus R, Culver DH, et al. Surveillance of HIV infection and zidovudine use among health care workers after occupational exposure to HIV-infected blood. The CDC Cooperative Needlestick Surveillance Group. Ann Intern Med 1993; 118:913.

Baggaley RF, Boily MC, White RG, Alary M. Risk of HIV-1 transmission for parenteral exposure and blood transfusion: a systematic review and meta-analysis. AIDS 2006; 20:805.