Well, since, as you mentioned yourself earlier in the thread, current estimates suggest that around 50% of the population is carrier of the herpes virus (which doesn't necessarily mean that they will pass it to others), I would think that there is a good chance that some SPs are carriers as well. I'm not convinced however that there are more at risk than the general population of being carrier. Based on my anectodal experience and some studies, I would actually believe that they are less likely to be carrier than the general population.
As others have mentioned, escorts (and I'm talking here of those who work in decent conditions, who aren't forced or pressured to offer certain risky services, and who are in a position to refuse to provide services to clients who display signs of unhealthy behaviours, lack of hygiene, and/or who show potential symptoms of STIs) tend to be more informed about safer sex practices and risks, and they tend to practice safer sex more rigorously than the general population. They also tend to get tested more regularly, and more thoroughly, than the general population and therefore get treated for any infections.
As I said, the above is based mostly on anecdotal evidences from my own experience and from what I have seen around me (both among my "civilian" friends and among other SPs around me). A
recent study done in the Netherland seem to align with this anecdotal evidence:
According to their analysis of the numbers of patients seeking treatment in 2007 and 2008 at three sexual health clinics in South Limburg in the Netherlands, they found that
I haven't read the study and don't know the detail of its methodology and whether these results can be translated for the Canadian population (given for instance the different laws and practice around prostitution and health care in the two countries). But those caveats notwithstandings, the study does seem to confirm trends that I have seen around me.
On another but related note: rather than thinking in terms of "what are the risks" to make your decision regarding your sexual activities, it is usually recommended that you think in terms of "which consequences I am ready to deal with"?
In other words, rather than making your decisions of what do to and with whom based on a theoretical risk factor and magical thinking (we tend to assume that the bad stuff won't happen to us), assume that your partner IS infected, and adjust your practices accordingly.
Not all STIs carry the same consequences and health risks. Some, like Chlamydia and gonorrhea are easily treatable, assuming of course that you get tested regularly and get treated early on should you get infected. Others, like herpes, can only be treated but can never be cured, but is more of a social nuisance than a health risk. And then you have some like HIV/Aids which while not necessarily a death sentence anymore in Canada, has considerable and damaging effects on your health and other aspects of your life. Not all those STIs are transfered in the same ways, and therefore some practices are more or less risky for different STIs. So, the questions is which STIs you are ready to take the risk of being infected with or not? Based on your answer to this question, adjust your sexual practices accordingly.
You are not ready to deal with being infected with herpes (assuming you aren't already)? Then don't have casual sex with strangers (whether SPs or civilians), inform yourself about what herpes outbreaks look like and avoid any contact with someone who shows those symptoms, and use barriers when having sex (dental dams, gloves, condoms), and talk to any new partner about their health history and sexual practices. But even all those precautions can only reduce the risk, not make it nul. Herpes can only be diagnosed through a swab if they are sores present. Blood tests currently available are not useful because they cannot tell you where on your body you have HSV. And as mentioned earlier, while barriers provide some protection, they don't provide full protection. And while in most cases, infections occur when a partner has an outbreak, sometimes people can be infected even when there are no sores—this is called asymptomatic shedding.