As @Askew said, HIV can only be passed from infected to uninfected, it does not occur naturally. Intercourse is not the only way HIV can spread, most bodily fluids will allow transmission, blood, semen, vaginal fluid, pre ejaculate and breast milk.
Like any virus it requires transmission from one to the other to spread.
HIV was actually something I really enjoyed studying.
@Common_Courtesy, at least some of us will have knowledge outside of technology.