[ACPlayer]

What exactly is your point?

I can 100 percent guarantee that 100 percent of heterosexual transmission comes from a partner who is HIV positive.

Every time you have unprotected sex with a partner you are risking HIV transmission (and other STD transmission). Make an assumption of the chance that a partner has HIV (say 1percent or whatever) and BZ can calculate for you what is your chance of being HIV positive after 100 or whatever contacts with HIV positive persons.