Oh and I especially liked this quote from one of the women they interviewed:
"
You're very unlikely to pick anything up by sticking your dick in someone's mouth, but you're very likely to pick something up the other way from letting someone stick their dick in your mouth."
That's supported by research: "Oral sex is considered less risky for the insertive partner than the receptive partner because the receptive* partner is only exposed to a partner's saliva."
https://www.ncbi.nlm.nih.gov/pubmed/11363199 (* sic for 'insertive')
So when people claim that the risks associated with unprotected oral sex are low, they should bear in mind
(1) that the research on how disease-free sex workers are, dates to a time when condoms were almost always used (in the wake of the AIDS crisis), and
(2) sex workers have a right to be concerned about risks to THEMSELVES: which are higher than the risks to the client.