Trying to advise a buddy but want to do it correctly

[jscs3142]

I know handjobs are not a risk even with saliva lube or even genital secretions. I was trying to ensure a buddy that I have been told repeatedly and seen many doctors agree. ( I think even cdc says that’s the case ) anyways he was asking me how do the “experts” know that?
I told him most say they have never seen a case and then he said “I’m sure many people don’t because”
A) have only those exposures alone ei during a sexual act most don’t stop their the progress further
B) if they do they don’t get tested in a clinic
C) I’m sure no studies have been conducted so how is their data etc

I wanted to advise him correctly…..I didn’t really know how to answer him other than all the experts I see so no way etc.

So my questions is this.
1) is this based on the fact that thousands of ppl come in after these exposures to std clinics etc and always test negative therefore coming up with conclusion that  a handjob is obviously no risk or very little risk etc
Or
2) is this just an assumption that experts have come up with based on science of transmission etc.

I understand now over my own recent anxieties that transmission just doesn’t seem to happen or atleast didn’t in my case.
He was just arguing with me what are the facts and data behind that statement etc and he kind of stumped me on what to say haha.

Anyways if I am going to help ppl out on advising them I just want to be factual….. maybe there are no facts behind and if so then so be it.

Just didn’t know if it something I could say like the following “ the reason it’s no risk is because no one has ever caught anything from such exposures and millions have been tested from them” ( basically proving it’s not possible maybe only theoretical) same thing as saying “ HIV is not a risk from oral sex because even after millions of people receiving oral sex no one test positive in an std clinic after exposure” even though it’s a rhetorical risk etc.

The short of it is can I say “ no risk for stds from handjob because many have been tested after exposures that way and no one has ever tested positive after such exposure in a clinic” is this an accurate statement? Or is just all assumed they wouldn’t test positive if the where to come test? Do clinics actually see and test ppl that have these kind of exposures?