While reading about sexually transmitted disease, I always wonder how much body fluid is actually required to transmit some diseases, specially in the case of other kinds of sex (masturbation, hand job, fingering and genital contact).
For example, this website list chances of getting STDs: Know your chances - Smart Sex Resource. Specially the table about other kinds of sex mentions that you can get gonorrhea and chlamydia from genital to genital contact, with sharing of body fluids. But exactly how much? Is there any literature on that?
I'm thinking in a scenario like: person A is fingering person B. Person B is infected with chlamydia/gonorrhea (easy to transmit). Person A has person's B fluid on his fingers/hands. Person A uses a towel to dry their hands a bit before engaging in "self" masturbation. What's the risk of person A getting infected?
I'm asking because anal/vaginal/oral sex without condom poses a clear risk, but sex isn't mechanical. People will kiss, finger and masturbate each other during sex and a tiny bit of fluid may be swapped.