I hail Stateside from Las Vegas, NV, whereat I drove a taxi for a couple of years. Had to learn the basic legal framework of the brothel industry so as to stay legal when providing transportation services. (Cross the line and you are a felon.)
Consider...
One issue on which NV _licensed_ working girls excel is medical. At the brothels nearest Las Vegas, Wednesday is Doctor Day. All contractors of the service persuasion are bussed to a local physician, appropriate tests administered, and a bill of health (clean or otherwise) is issued. The Industry claims that there have been exactly zero cases of HIV traced to a licensed, er, Entertainer.
Regarding the actual Entertainer's Card, details can be found here:
http://www.lvmpd.com/Permits/Work_Cards/Non-gaming.html
This is nothing out of the ordinary for Nevada. To do essentially anything on a commercial basis one needs a sheriff's card. The office that processes these permits effects the arrest of eight to ten applicants per day... related to me by an employee.
(Note: It is a misconception that prostitution is legal in Las Vegas. In fact the state law is written in such a way as to exclude Clark County (Las Vegas) and Story County (Reno/Sparks) from those counties which may vote to approve this activity.)
In any event, I see little evidence of such an HIV-protection mechanism in the LOS. Or am I missing something?