Risk of HIV infection after one "sort-of unprotected" encounter

[veryterrified]

Dear Doctor,

I will try to be as specific as possible.  I am a disease-free 29-year-old white male in New York City.  Two days ago, I had sex with a 30-year-old Brazilian female who has been living in NYC for the past several years.  We had both vaginal and anal sex for about 2 hours.  I was wearing a condom the whole time and would occasionally replace it with a new one as we took short breaks.  HOWEVER, at one point during anal sex, the base of the condom began to ride up my penis and slipped off.  I inserted my penis back into her anus and had unprotected anal sex with her for about 10 seconds before pulling out and putting a new condom back on before continuing.  I have no idea about her sexual health, but to be conservative let's assume she was HIV-positive.  What is the probability that I am infected?  I have read on the internet that the per act risk for unprotected insertive anal sex with an infected partner is something like 6.5/10,000, or .00065 (.065%).  This seems extremely low.  Is this true?

I will wait 3 months to get tested (so the antibodies have time to appear), but I am very nervous and would be very grateful for any information about my chances.

We also had unprotected oral sex and my tongue was inside her anus for a few minutes, but I understand that this in and of itself is no cause for concern and not reason enough to get tested.  At least it won't increase the overall probability of infection, correct?

Thank you very much for any thoughts.

[Edward W Hook, MD]

Last answer.  

1.  There are no studies on the duration of exposure.  It is logical however that shorter encounters hould be lower risk.  

2.  Your calculation is correct.  Let's not play the "have you ever heard of" game.  The odds are numerical values.  

the thread is over.  EWH

[veryterrified]

Thank you, doctor, for clarifying.  Final follow-up:

1) Do you have any opinion as to the extent to which my odds of contracting are lower because the unprotected exposure lasted only 10 seconds?  In other words, how do experts define a "single-exposure"?  One that lasts 1 minute, 10 minutes, 1 second?  I realize there are many many variables at play here (her viral count IF she happened to be infected, etc.), but I am trying to quantify my risk to the extent possible as I'm very very nervous and quantifying the risk seems to be the best way to help me deal with this.

2) I do not believe she is a CSW, but if she were, then you say her chances of having HIV were 1 in 100.  Coupled with the 1 in 200 risk because of my exposure to her, that puts my odds at 1 in 20,000 of contracting, and that's assuming a "full-length exposure" (however long that is).  Correct?  These odds seem very very low.  Have you or your colleagues ever heard of someone contracting on these odds?  You say I should not be "terrified," but what level of concern would you say is appropriate here?

Thanks again so much.

[Edward W Hook, MD]

If I said 1 in 2000 exposures to an infected partner through rectal sex results in infection in an earlier post it was a typo and I apologize to that person.  The risk of getting HIV IF a partner is infected for vaginal intercourse is 1 in 1000-2000.  For the insertive partner in rectal sex it is 1 in 200.  

The recommendations for testing at 3 and even 6 months are the result of two factors- data from older tests no longer used (you really do not need to worry about which generation of tests you were tested with, at this time virtually all tests are far more sensitive that they were even 2-3 years ago when the 3 month recommendation was made) and secondly, the fact that some mostly governmental agencies which have to provide recommendations for virtually everyone without the sort of interactions such as those you get with your doctor or n-on personalized sites such as this, feel the cannot "afford" to be wrong and therefore make recommendations and guidelines which leave most people unnecessarily nervous for 4-6 weeks longer than the 6-8 weeks it takes virtually everyone to develop HIV antibodies.  

that your encounter occurred in NYC was considered in my answer.  EWH

[veryterrified]

Dear Doctor Hook,

Thank you very much for your prompt response and for this great service.  I appreciate your time and will make every effort not to waste any of it.

Just a quick follow-up to clear up a discrepancy.  In your response to me, you said that many experts would put the risk for someone who engages in a single act of unprotected insertive rectal sex with an infected partner at 1 in 200.  However, in a more recent response to another post (responding to ashley77783), you refer to the chances of getting infected from a single act of unprotected insertive rectal sex at 1 in 2000.  I'm hoping you accidentally left out a zero in your response to me?  That is a big difference in probability.

Also, the CDC claims that waiting 3 months to get tested will detect 97% of infections, but to detect 100% of infections one should wait 6 months.  In your posts on the site, you seem very confident that waiting 6 months is excessive for conclusive results.  Why such a large gap between your and the CDC's recommendations on this point?

Finally, how does the fact that this happened in New York City affect these standard statistics that I am seeing on the forum?  NYC must be a higher risk location and therefore skew the probabilities, no?

Respectfully,
slightlylessbutstillmildlyterrified

[Edward W Hook, MD]

Welcome to the Forum.  You should not be terrified. Your risk for HIV from this series of exposures is quite low.  For starters you say "let's assume she has HIV".  Well, that is a rather silly assumption. The chance that she is HIV infected is very low, perhaps 1 in 100 if she is a commercial sex worker and even lower if she is not.

Now let's analyze your activities.  Your only meaningful exposure is your brief unprotected rectal intercourse.  Your oral sex is virtually no risk, no matter where your tongue was.  As for rectal sex, for the insertive partner many experts would put your risk , IF she was infected, at 1 in 200 following a single episode of unprotected rectal intercourse.  In your case, the exposure was also quite brief making infection even more unlikely (longer exposure- higher  risk).  

So, what you do.  first, understand that your risk is low.  Second, if possible, the fastest way to find out about your risk is to see if she will get tested.  If she will and it tested and found to be negative, no risk.  If she won't get tested or you cannot locate her, then for you, an antibody test for HIV at 6 weeks following exposure will detect over 95% of infections while at 8 weeks virtually all infections can be detected.

Bottom line, your risk is not very high.  Try not to worry. When you do get tested, also remember to get tested for other STDs like gonorrhea and chlamydia since they are more common than HIV.  

Finally, don't let this unfortunate event keep you from continuing to use condoms in the future. They are still a great way to prevent STDs, including HIV.  Take care.  EWH

[veryterrified]

Dear Doctor, I should also add that I am circumcised.