The U.S. Centers for Disease Control and Prevention (CDC) has produced estimates of per-act risk of transmission of HIV for a variety of sexual and other exposures. Regarding sexual exposures, the highest risk is for receptive anal intercourse, with a risk of 138 infections per 10,000 exposures. The risk for insertive anal intercourse is 11 per 10,000 exposures while the risk for oral sex approaches zero.
Parenteral exposures have higher risks of infection. The risk of needle sharing for drugs of abuse is 63 per 10,000 while the risk to healthcare works from needlestick injury is 23 per 10,000.
The highest risk events are blood transfusion with contaminated blood and vertical transmission (mother-to-child) at 9250 and 2260 per 10,000, respectively.
Reference:
Patel, P., C. B. Borkowf, J. T. Brooks, A. Lasry, A. Lansky and J. Mermin (2014). "Estimating per-act HIV transmission risk: a systematic review." AIDS 28(10): 1509-1519.
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