There is a fair amount of research done by various medical bodies in Oz which have concluded that sex workers are no more infected with STD's than the general population. In fact if Street workers, Transvestites and Aboriginal sex workers are excluded, the incidence of disease in the remaining workers is marginally less than the general population.
A tranny in WA was prosecuted and imprisoned for infecting a client with HIV through unprotected sex. 'She' served time in prison - a men's prison!