I'll skip a lecture about your decision to have unprotected anal sex with a male (anatomically) sex worker. I understand alcohol was involved -- but please not again, OK? That said, I'm very glad to hear you discussed her HIV status with your partner before having sex. That's a critically important and highly protective approach, because most people are truthful about their HIV status in such situations. Therefore, your partner's saying she was on PrEP probably is accurate; and that in turn implies she doesn't have HIV. In that circumstance, there really is little if any HIV risk for partners. I can't argue strong against you being prescribed PEP, but I don't really think it was necessary. Of course that assumes the truthfulness of your partner's information, and I can understand why you (and the prescribing doctor) might not trust it.

As for timing of PEP, there has always been consensus that an earlier start (within 24 hours) is best and that effectiveness probably wanes after that. Real-world data in humans on efficacy of PEP at various intervals after exposure are almost impossible to collect and analyze with confidence, and animal studies are the backbone of available data. However, I cannot comment on the particular study you cite. Previous ones indicated at least substantial efficacy of PEP out to 72 hours, even if this study did not have that result. However, there are extremely few reports of PEP in humans failing to prevent HIV, so given the millions of courses of PEP treatment that have been administered after sexual exposures, the risk of PEP users becoming infected obviously is very low. Undoubtedly this reflects the combination of low risk of many people who probably didn't need PEP anyway, plus the inherently low risk of HIV transmission from most exposures. (If your partner had untreated HIV, then even without PEP, CDC's calculation is that transmission risk is 11 infections per 10,000 exposures, or one chance 909.) (https://pubmed.ncbi.nlm.nih.gov/24809629/) 

Once someone has started PEP, we on this forum are not in a position to advise about continuing or stopping it. However, you might discuss this with the doc or clinic where it was prescribed. One approach that would provide certainty is to contact your partner, if you are able to do so, and ask her to be tested for HIV. If confirmed negative (as expected) you would know for sure you were not exposed. Even without that, you might think about a downside of PEP that both patients and doctors often forget:  PEP prolongs the duration of anxiety, because conclusive HIV testing is delayed to at least 6 weeks after the last PEP dose, and some experts advise three months. So instead of a conclusive negative test 6 weeks after exposure, you will not be 100% certain you weren't infected for at least a couple of months from now.

I'll close with a guesstimate of risk in response to your last question (how likely I am to go to test positive...?). I would say under one chance in a million.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD

With that said, despite the prolonged period before being able to receive a conclusive result, given the point you made about millions of PEP incidents leading to very few failures I think I will see the remainder of the course through. 

I have also seen that trans women are on the higher side of risk (42% on trans women infected in certain cities); although this woman seemed to be very aware as she told me numerous times she was on PrEP. 

Additionally, I did some research on the latest stats within NYC, and based on the numbers and her ethnicity (she is white - saw this demographic of trans women has an infection rate of 17%) I am hopeful the likelihood of infection is lower.   

Here is the link to the latest NYC numbers:

Can you extrapolate on how your arrived at the guesstimate you provided? I’m hopeful that I have been lucky in this instance, but again your point is well taken and I don’t plan to play with fire again if I’m fortunate enough to come out of this unscathed.

In looking at the numbers around rates of infection for trans women it isn’t out of the realm of possibility that she may have been infected. How would these numbers change if there was a 25% chance she was infected and not on treatment? In other words, assuming she wasn’t truthful and the we estimate the likelihood that she was infected to be around one in four. 

I’m trying to keep my anxiety in check and hope for the best, while also planning for the worst possible outcome. If you can help me in that by walking me through this scenario it would be greatly appreciated. 

Also, if possible to keep this thread active so that I can report back on my next test (which I anticipate around mid-August, as I finish PEP treatment at the end of this month) that too would be appreciated! 

Thanks for all your help and all you do! 

Threads are closed after 1 month or two follow-up exchanges, whichever comes first -- and that's where we are. And what's the point of tell me that you have completed PEP? Or posting a negative test result? All I would do is figuratively nod and tell you to trust the result. But I'll make a deal with you:  in the exceedingly unlikely chance you test positive, come back with a new question to let us know and we will reimburse your posting fee. We certainly would want to know, because you would be the first: in the more than 15 years of this and our preceding forum at MedHelp, with thousands of questions from persons worried about catching HIV, not one so far has turned out to been infected. If and when it that happens, I am confident it will be from a questioner with far higher likelihood of being infected than you.

Please do not post any additional questions about this exposure. There's nothing more we will be able to add to what you have already heard.

* And let's put that 1 in 200,000 risk into real world context. The National Safety Council (whose website you can easily find) says that one in 1,756 Americans die from accidents (car wrecks, drowning, falls, etc, etc) every 12 months. That means the chance you will die of an accident by this time next year is 113 times higher than the chance you will have HIV, even at the high HIV risk level you asked me to calculate. (200,000 divided by 1,756). So I would say stop worrying about HIV, but don't forget to use your seatbelt!