HIV - Prevention Expert Forum
Probability of contracting HIV
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This forum is limited to prevention of HIV and to safe sex in general. All questions will be answered by H. Hunter Handsfield, M.D. or Edward W Hook, MD.

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Probability of contracting HIV

A couple of days ago, I had unprotected vaginal sex with a woman I did not know in the Boston area. She was a white woman and said that she was 27 years old. I have no idea if she was HIV-positive or not, but I found out the morning after that she was homeless. To say that I am terrified right now would be an understatement. I can't eat, or sleep, or even think clearly anymore, even though I asked her if she had any STDs at all, and she said no. Would you say that this was a high-risk encounter, and if so, how long do you think I should wait to get tested?
239123_tn?1267651214
Welcome to the forum.  Thanks for your question.

My first advice is that you get into the condom habit for new or casual sexual encounters.  What were you thinking???  But still, the likelihood is very low that you caught HIV.

Homeless or not, the chance your partner has HIV probably is low, especially if she is not a current or past sex worker or injection drug user; and for the most part, people are truthful when asked about HIV status.  And even if she were infected, the transmission risk is low for each episode of unprotected vaginal sex; one estimate is 1 transmission for every 2,000 exposures,

So I'm not especially concerned about HIV. However, the risk of other STDs could be substantial.  Be on the lookout for urethral discharge (pus or mucus from the penis, sometimes but not always with painful urination), and for penile sores or blisters and of course get checked right away if anything shows up, preferably at an STD clinic.  Even without symptoms, it would make sense for you to be tested for gonorrhea, chlamydia, and syphilis.  The first two can be tested on urine any time more than 2-3 days after exposure; the syphilis blood test needs to wait until about 6 weeks.  And although the risk of HIV is extremely low, I would also recommend HIV testing at 6 weeks.

Best wishes--  HHH, MD
12 Comments
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Avatar_n_tn
Thank you for your quick response. I just wanted to know, however, whether there is a particular HIV test you would recommend--for I know that there are more than one--that I could expect to be authoritative after 6 weeks only.
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239123_tn?1267651214
The best test is usually a duo test, for both HIV antibody and p24 antigen, and is 100% reliable any time from 4 weeks on.  However, it isn't offered by all clinics.  Other than that, any laboratory based antibody test at 6+ weeks is as good as any other.  I would avoid the rapid (while you wait) oral fluids test, which takes the longest time (up to 3 months) to achieve maximum reliability.

Or just visit your local public health STD clinic and follow their advice.  They won't steer you wrong.

See http://www.medhelp.org/posts/show/1704700
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Avatar_n_tn
I'm sorry to have to bother you again with my questions, but this is my last one, and that's it. I've read that there are instances in which, after a possible exposure to HIV, a doctor will prescribe HIV drugs to a patient even before they test positive, so as to reduce the chance that they contract the disease. Would you recommend that I do that, that, if possible, I should go ahead and begin taking HIV drugs now?  
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239123_tn?1267651214
You are referring to post-exposure prophylaxis PEP) with anti-HIV drugs.  Local guidelines vary, but in most communities the exposure you describe would not meet standard criteria to recommend PEP unless your partner were known to be infected or at especially high risk, such as being a commercial sex worker or injection drug user.  In any case, it's probably too late; PEP is not believed to be effective unles started within 72 hours of exposure to HIV.  You definitely should not seek out or take anti-HIV drugs on your own; if it has been less than 72 hours and you want to pursue the possibility of PEP, you'll need to see a doctor or clinic about it.  Most urban emergency departments and urgent care clinics are up to speed on local recommendations; or, as suggested above, you local or state public health STD clinic.
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Avatar_n_tn
Sorry, I know I said my last question was the last one that I would ask, but I have one more, and then I am truly finished. Basically I want to know if an "RNA test" for HIV is the same as the "duo test" that you have recommended.
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239123_tn?1267651214
RNA and DIY are different tests.  But the combination of tests you had is equivalent to the duo test.
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239123_tn?1267651214
That's RNA and duo.
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Avatar_n_tn
Sorry, I ought to have been clearer. But what I meant to ask was whether the RNA is just one of the two components to a 'duo' test, or whether it is an entirely different test altogether.
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239123_tn?1267651214
The antigen component of the duo test is different from RNA testing, but works the same way.  Both are direct tests for the virus, as opposed to antibody, which detects the immune system's response to the virus. If you want early reassurance, I would recommend 2 duo tests, the first at about 10 days (instead of RNA) and a second at 4 weeks.  If both are negative, it will be just as reliable as having an early RNA test plus a later antibody test -- and a lot less expensive.
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Avatar_n_tn
Hello.
I'm sorry to continue this thread after so much time, but I wasn't sure who to contact regarding my problem. I've looked at my bank account statement, and it seems I've been charged $22 twice by medhelp, even though, as my profile history clearly shows, I've only asked one question instead of two. So I should only have been charged once. Perhaps you might help me resolve this issue, or direct me to someone who can?
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239123_tn?1267651214
Use the Contact Us link (at the bottom of the page) to leave a message with MedHelp administration.
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