I tried to post my questions with specifics related to my situation but the website said my post was too long, so here are my questions without much context. It is worth noting that I am a gay man and my questions are the result of multiple sexual encounters with the same man.

1. Let's say someone was infected with HIV a week or two before starting PREP--such that the HIV test they give you right before prescribing  PREP came back negative because it was too soon--Would starting the PREP cause this new HIV infection to be undetectable on subsequent HIV tests? I'm basically worried that I got HIV due to a blood-in-the-mouth exposure about a week and a half before starting PREP, and that I will come back negative on subsequent HIV tests even though I'm positive because the PREP is suppressing the infection and making me undetectable.

2. Am I right that if you perform a rim job on someone and get some blood from their anus in your mouth, that would be low to no risk for HIV? 

3. If a person has known anal chlamydia, can you get it in your mouth from rimming them?

1.  Most PrEP regimens contain medications active against HIV and, as such could delay detection of infection but they would not prevent detection of an infection which was incubating at the time PrEP was begun.  Subsequent tests would be positive, probably at times more than 6 weeks after the exposure of concern.  remember that persons who are undetectable on therapy still have positive tests.   I should add however that this is quite rare- few people acquire HIV during that relatively short interval.  Remember, HIV is acquired through oral exposures on average less than once every 10,000 times a person is orally exposed to infection.

2.  Correct.  rim jobs are very low risk exposures.

3.  For reasons that are biologically unclear, oral chlamydial infections are relatively rare.  Thus while you might get chlamydia from rimming a person with rectal chlamydia, it is uncommon.  If you were exposed, throat swabs for chlamydia would provide accurate results any time more than 4-5 days after an exposure.

I hope this information is helpful. EWH

If you don't mind, I am going to quickly relay my three experiences with this man that I am concerned about just to get your input as it relates to my specific circumstance

ENCOUNTER 1-A month before PREP: We had condom protected anal and unprotected oral (both gave and received).

ENCOUNTER 2-A week and a half before PREP: Protected anal/unprotected oral just as before. My friend had noticeable amounts oh his own pre-cum on his fingers from touching his penis which he then used to finger my anus. I am not sure if that is a big deal.

ENCOUNTER 3-Four days into PREP: Protected anal/unprotected oral just as before. This is the encounter where I thought I tasted blood in my mouth from rimming him. 

I believe the condoms were all intact/functioning properly for all three of these encounters, but you never know. 

I wasn't all that worried about HIV until he called me yesterday and told me he had anal chlamydia. I immediately started freaking out about what if he has HIV, too? I went to urgent care this morning and they put my on Doxy. preventatively 

Just to be 100% clear-Am I right that if I acquired HIV from any of the above incidents it will show up on future HIV tests even though I am on PREP? Or will I have to stop PREP in order to get an accurate HIV result

Thanks again!

1.  Have confidence in your condoms.  When condoms fail, they bread wide open leaving no doubt that they failed.  As long as the condom covered the head of the penis and was worn from start to finish, you were protected.

2.  In encounter 2, HIV and other STIs are not effectively transmitted when genital secretions are on a persons hands which are then used for masturbation.

3.  Chlamydia is much much more common than HIV.  That he had chlamydia does not mean he has HIV.

The best way to resolve your concerns is for him to be tested.  If his test is negative at this time, then he could not give your HIV during the encounters you describe (if he is not, it also sounds like, as his friend, he would benefit from having PrEP recommended for himself too).

Please do not stop PrEP.  A test in another month or so will provide accurate information and also conclusively prove that you were not infected if he is not willing to test.

EWH

One last very quick question and then I realize I have reached the end of my allotted answers:

As far as the incident that took place while I was four days into PREP---where I may have had blood from his anus in my mouth---Do you think I can trust subsequent HIV tests with regard to this particular incident? I am a little confused about this one because, as I mentioned, I was actually ON PREP for four days when this happened. Im worried I was on  PREP long enough to render me undetectable but not enough to actually prevent the virus from taking hold, and that my next test will be negative, even though I'm actually positive, because of the PREP.

Thank you for humoring me with this. As you can tell, I've gotten myself extremely anxious. I greatly appreciate your time and expertise!

As you know, this completes this thread.  Your risk for HIV from the encounters you describe is virtually zero.  Please don't worry.  EWH