[Question #9241] PREP Risk Window Period

34 months ago

I’ve been on Truvada generic prep for the past couple months and have been taking it consistently. It has been good so far and I have tested negative for hiv during the regular checkups and have been using condoms except for one time during my early days on prep and now by mistake. I’ve been more worried about my latest encounter of receptive condomless anal, he claimed to play safe and we started with condoms, that condom broke and we just continued without because of my prep. I took an extra pill of my medication that night after just in case. I know statistically I should be fine as prep is effective, however I’ve recently been reading about some breakthrough cases and this got me worried. I’m in Canada if it makes a difference. Would you know the likelihood of this person not only being positive but also positive with a prep resistance strain?

It’s been just over a week since the encounter, I was wondering if you think I should get an RNA hiv test done next week? Would prep have any effect on the window period of this test? I will for sure test next month with a 4th gen test, but again am worried about the window period. My regular test is scheduled in 3 months. I am going to avoid anal until then.

Edward W. Hook M.D.

34 months ago

Welcome to the forum. Thanks for your questions. Thanks as well for your decision to take Truvada PrEP. It will do much to keep you safe. I note that your partner stated he was not infected and in our experience, most people tell the truth about these matters.

As for testing, when to do it is unclear. While rarely infections do occur for persons taking PrEP, these remain quite rare And infection with prep resistant strains is even less common. I would have confidence in the effectiveness of your PrEP. At the moment however breakthrough infections are so rare that it is difficult to comment on how the period between exposure and a positive test would occur.

Your leveling of concern and anxiety will determine when and how often you test however, my advice however I would be to not be overly concerned and simply suggest testing again in about a month as planned. Alternatively, if you can contact your partner, and if he would be willing to test, you can resolve this question completely. If he tests negative with a fourth generation tested this time, you are certainly in the clear.

Hope this perspective helps. EWH

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34 months ago

Thank you for the response. It seems like I shouldn’t worry too much, but unfortunately I am having a very hard time mentally with this whole thing. I think it stems from not having a clear window period for testing like I would have had without PrEP.

If I stop taking my daily Truvada, will a 4th gen test after the normal 6 or so weeks after the prep be conclusive? It’s been about 2 weeks since the encounter, is it safe for me to stop the prep or should I wait the recommended 28 days. Would you recommend against an RNA/PCR hiv test? I’ve heard of a higher rate of false positives on these, plus are they ever reliable to conclude negative hiv? And if so after how long?

I think after some risk calculation I shouldn’t worry because the risk is low from my understanding that he would have HIV in the first place.

Edward W. Hook M.D.

34 months ago

The reason there is not a “clear window” is the same as there is no “clear window” associated with condom protected sex- use of condoms and PrEP make you risk for infection virtually zero. While if you were to stop your PrEP, results of a 4th generation test at 6 weeks would probably be conclusive. PCR tests would be positive sooner but, in my opinion, your risk from the encounter you described, I see little reason to worry, to do more than routine testing, or to stop PrEP.

I really think you do not need to worry. EWH

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34 months ago

Sorry maybe I didn’t describe properly in the original question. The encounter was me bottoming without a condom, so I was (and still am) on daily PrEP at the time, the encounter itself was not protected by condoms. I assume this doesn’t increase the risk level too much since PrEP is effective even without condoms? We had started with a condom but it broke and continued and finished without the condom unfortunately.

I appreciate the feedback you have provided.

Edward W. Hook M.D.

34 months ago

I understood the question. PrEP is very, very effective for HIV prevention, even in the absence of a condom. The encounter you described (unprotected bottoming) was a virtually no risk event in terms of HIV risk. As a result, there is really no need for specific or special testing other than the routine testing that is typically done for persons on PrEP.

Thanks for your thanks. As you know, we provide up to three responses for each client's questions. This will be my final response and the thread will be closed shortly. Take care. EWH

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