I don't think many are going to want to burn their alias over this either.

I don't know anyone who has, and I haven't myself. In the civvie world, where I play often enough, I've never had a CBJ, never had a problem. I've also never been asked to use a dental dam when going down on someone, again, never had a problem.

 
So to answer your query, it's rare. The CDC says it's possible, but very unlikely. Bacterial infections are much more likely than viral infections, but are still a long shot. You have to remember, bacteria have evolved to live in a certain environment, so when you take them out of that environment, they tend to not do well.  

Viruses need bodily fluid to blood contact in order to spread, so you essentially need a sore on your dick and a cut in the providers mouth/throat in order to have enough viral load to successfully transfer, so easily preventable there provided the provider knows to look at it before putting it in her mouth.  

The reason I'm thinking that CBJ is such a big thing in p4p is that, at least everyone that's younger than 30 or so, was fed the gloom and doom sex ed in school. The way it was taught to me was that if you had sex you would probably get the herp and die of aids after substantial pain, and that condoms were 50/50 in preventing said certain death, but you'd probably still get the herp and be undesirable to women forever.
This is obviously not the case, and admittedly, the CDC itself still pushes this puritainesque agenda, but when you read the actual studies they're citing, it's obvious that the risks were overblown, particularly with condom use.

How many mongers have caught STDs from BBBJ. This would be assuming that FS is always covered.  

I know that I have not.

Been in this hobby for over 20 years. I only get a CBJ if I misread the providers offering or she lies about it.
Never had an STD. (tested regularly).  

As a previous poster mentioned, STDs to a healthy male from oral is highly unlikely. If there are no obvious sores in his penis or her mouth you will have a better chance of getting hit by lightning.

that have been around longer than a year have something or have gotten something.  The most common being yeast infections, chlymidia or herpes.  A lot have HPV and aren't aware of it.  A lot of the diseases are asymptomatic for awhile.

I see providers will do BBBJ then CFS, that always confuses me because it's intercourse either way. As far as BBBJ goes , the provider (female) is at higher risk to receive an STD where as BBFS is mutual. A provider can catch an STD from the bodily fluid a man leaks during a BBBJ (precum), So there doesn't need to be a bump or cut . To top things off if a guy has chlamydia or gonnorrhea, their leaking smells . Just a FYI lol I've had a guy who I was going to do a CBJ on .. he had the drippy odor. I ended the session.