Assuming the writer is focusing on sex with prostitutes;
Be aware that they can get 'Prem' (?) or is it 'Prep', at their GUM clinic visits these days, so (and I'm no medic) they can do UTC Bareback if they want, and there are for sure those WG's that do, for their 'selected regulars', but they can pass HIV on to others perhaps avoiding it themselves.
As for all the other STDs that are around, i think you can get quite a few of them from various permutations of oral sex. If she's a busy/ conveyor belt provider then when you snog her on arrival she may have had another mans cock cumming in her mouth ten minutes earlier. If she's a barebacker, UTC or otherwise, then your are not that removed from giving that previous client a blow job when you give her oral sex. Whatever lurks in her mouth is soon on your cock when she gives you OWO.
Of course Bareback/ unprotected sex with a prostitute is not 'safe'. Using condoms for penetrative sex will go a long way to controlling the risks of getting an STD. If you want to fully control those risks then don't go to a prostitute.