Keep in mind that a lot of hemophiliacs got infected by HIV-contaminated blood before we knew about AIDS. What new diseases are currently spreading around the gay community which we don’t have tests for yet? Who knows.
It’s also likely that they had a part in helping develop the antiobiotic resistant strains of gonorrhea and syphillis, given the disproportionate spread of those diseases amongst their ranks as well. So another possibility out there is that we could see a new variation of an existing STD that is resistant, if not immune, to the medical treatments for it thanks to rampant, wild, behavior on their part.