On average, you have a 1 in 1,000 chance of contracting herpes by having unprotected sex with an infected partner. Condoms reduce the chance by at least 50% and probably more like 70-80%. While no one can guarantee you did not catch herpes from this encounter, the odds are in your favor that you were not infected, assuming the sex worker did in fact have genital herpes. Congratulations on using condoms and practicing safe sex.