I met a CSW in Bay Area of California - Korean lady , 25yrs. She did not have any visible signs of sickness or infections. She is from an organization where all the CSW provide an option of uncovered vaginal sex. The do screen for race and age. 

Q1) we had unprotected oral sex, followed by brief ( 5 to 7 seconds ) unprotected vaginal sex. I used condom after that. What are my chances of catching an STI/STD due to the brief unprotected sex?

Q2) I am uncircumcised 29 yrs old, would this put me more at a risk?

Q3) This incident happened about 24 hrs ago. Would you suggest PREP for me? or any other testing / medication.

Q4)  I heard that these CSW are always on PREP and most likely not very infectious. Is my understanding correct?

Thanks

Welcome to the Forum and thanks for your question.  I'll do my best to help.  The encounter you describe was low risk for acquisition of HIV.  Most CSWs even in a city like San Francisco do not have HIV and even in the unlikely circumstance that your partner was infected and not on treatment (effective treatment makes people with HIV non-infectious to others), your risk for acquisition of HIV would be less than 1 infection on average per every 1200 sex acts.  Further if your partner was part of an organization or organized group of CSWs it is more likely than not that she was tested regularly for STIs and was not infected.  As for your specific questions:

1.  The only STIs acquired from receipt of unprotected oral sex is gonorrhea or NGU and they are uncommon. The brevity of your unprotected exposure also may reduce your risk for other STIs.  If you are concerned however, you should be tested.  Tests for gonorrhea and chlamydia will be accurate and conclusive about 3 days after your exposure.  I anticipate that if you test, the results will be negative, proving that you were not infected.  Blood tests for HIV and syphilis (both very unlikely) take longer to be reliable and will not be conclusive until 4-6 weeks after exposure.

2.  Being uncircumcised does slightly increase your risk for infection in the unlikely circumstance that you were exposed.

3.  If you approached me requesting PEP, I would not provide it as I believe your risk in not sufficient to warrant PEP.

4.  I cannot comment on whether "most" CSWs are on PrEP or not although it would be logical and good idea for them to do so.  Prep is close to 100% effective in preventing acquisition of PrEP.

I hope this information is helpful.  EWH

I don't see any symptoms since the incident. Can I resume having sex with my partner with out the fear of any STD transmission?