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. Author manuscript; available in PMC: 2014 Jul 10.
Published in final edited form as: Eval Rev. 2010 Feb;34(1):19–34. doi: 10.1177/0193841X09353534

Figure 1.

Figure 1

Risk (probability) of acquiring HIV or a highly infectious sexually transmitted infection (STI) from a potentially infected partner, as a percentage of the risk associated with a maximum of 25 unprotected sex acts. For highly infectious STIs, risk grows rapidly in the first several sex acts and then more slowly as saturation is approached. For HIV transmission during receptive vaginal or anal intercourse, the per-partnership risk is essentially a linear function of the number of unprotected sex acts with that partner.