I refer the original questioner to the following reference:
Alexa E. Albert, David Lee Warner, and Robert A. Hatcher: "Facilitating Condom Use with Clients during Commercial Sex in Nevada's Legal Brothels", American Journal of Public Health, 88(4), 1998, pages 643–646
...which says in effect, that reseach has found that legal sex workers who contract STDs invaribly do so outside the brothel, the problem being identified when they fail the medical check required _before_ they return to work.
Feel better now?