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Avatar universal


Hello Doctor:

I am a male, 27, living in South Florida and I had unprotected oral sex both ways with a woman(I performed unprotected cunninglingus on the woman, and she performed unprotected fellatio on me) and we also had protected vaginal sex using a condom, back on November 12, 2005. I have been extremely worried if I contracted HIV from this woman, due to mainly not knowing her story, and this incident being a one night stand.

I was tested at 3 months for HIV 1 & 2 and thank God negative, and I was tested also at just over 6 months for both HIV 1 & 2, and thank God again, negative.

The CDC officially states that 97 percent test positive by 3 months, and in the rare occasions it can take up to 6 months. I spoke with a CDC representative and they stated that there have been cases where HIV has taken longer than 6 months to come out.

How rare are these post 6 month positives?

Doctor H., at this point, after testing negative for HIV 1 & 2 after 6 months, are their any chances that I could have either HIV 1 or 2, and it just has not come out yet? Or can I pretty much forget this and just move on?

I really appreciate your help.

Thank you, wantcomfort
13 Responses
239123 tn?1267651214
Indeed it is long since time to "forget this and just move on".  To my knowledge, there are no good data on the numerical risk of a false negative test result at 6 months; it's too rare even to study accurately.  Certainly no more than 1 chance in 100, probably less than 1 in 1000.  But since your risk of acquiring HIV from the exposure you describe was zero, it  doen't matter.

Calculate the odds.  Assume a 1% risk your partner had HIV (probably it was lower risk than that, actually).  Now assume the likelihood of infection from the exposures you describe, which absolutely is no higher than 1 in 10,000 (if she was infected).  Now assume a 1% chance of negative result at 6 months.  The odds you have HIV despite your negative 6 month test is therefore 0.01 x 0.0001 x 0.01 = 0.0000001.  That's 1 chance in 10 million.  The lifetime risk that a US resident will die of a lightning strike is 1 in 28,000.  That's 357 times higher than the likelihood you acquired HIV during the exposure you describe.  Since your actual risk for all those data points probably are at least 10-fold too high, your actual odds of having HIV probably are closer to 1 in 10 billion.

In other words, zero.  You have put far too much emotional energy, time, and money into this non-risk event.

I hope this helps reassure you.  Good luck--  HHH, MD
Avatar universal
Oops.  I miscounted my zeros.  0.01 x 0.0001 x 0.01 = 0.00000001 (8 decimal places, not 7).  So the worst-case scenario is a 1 in 100 million chance you have HIV after your negative 6 month test, not 1 in 10 million.

Avatar universal
Hi there... thanks for the great work doc.  The numbers crunching really helps a lot.  Im trying to calculate my bad luck lottery odds.  Probably out of sheer morbidity like the rest of us suffering from C.G.A.A.P. (Christian Guilt Aids Anxiety Phobia) :) Anyway. I had unprotected breif 2 min anal with dude... could u help me calculate my bad luck odds?  Then u are done with me I promise! I figured it at around 1/4000 which is not so cool.  Using the situation i described, the 3 month neg. test. and the probability that some dude offering himself thru a glory hole unbeknownst to me (thought it was oral, man was i mad when i figured out what he was doing)... Thanks... Keep up the good work... you must feel a bit like sysiphus, rolling the rock up the mountain and knowing it will fall to the bottom each time... sorry!

Avatar universal
yeah, right another example of random use of various odds etc.

just think about it. if as much as 3% of positive cases would not be picked up at 3 months and assume that roughly 10% of population tests yearly and that only 1 in 1000 of those who test is truly positive (probably a little higher). Assume further that 50% will stop testing at 3 months (also high given the official recommendation of 3 months). This means that in a country populated with 300 million people (roughly the size of the US) around 450 positive cases would be missed each year...30 million * 0.001 * 0.5 * 0.03. if every one stack to the 3 months guidleine 900 cases would be missed.

Now recall that the 3 months rule has been applied in Europe for 10 years now with no reported cases of failure (see e.g. the UK guidelines http://www.bashh.org/guidelines/draft/hiv_testing_2005_draft5.doc ).

So what good does it do to say that up to 1 in 100 positive case will be missed by testing up to 6 months...

surely this is not consistent with the almost 100% sure at 6 weeks.

I am closer to beleiving in the 6 weeks / 3months guidelines but am sometimes upset by seeing things like up to 1/100 will not be detected by a test at 6 months.

I said this in the past I would suggest a more careful use of odds for calculation of risks.

all the best
79258 tn?1190634010
1/100 chance = 1% (and as he noted, it's probably much less), which is close enough to 100%. And if you factor in the risk factors of the precipitating event, the chance of a false negative at six months is truly astronomical. Reread Dr. Handsfield's replies. But in any case, I have a feeling statistics don't matter to many/most people on this board; regardless of the actual risk, everyone thinks he'll be the one out of 10 million who actually has (whatever) happen :-)
Avatar universal
Hello Doctor:

Thank you so much for your help. It definately provides much more reassurance.  

I just wanted to clarify one thing. In your response to me, when you state in the Second paragraph:

"Now assume a 1% chance of negative result at 6 months",  

Does this mean that for your calculation you are assumming a 1% chance that the test result would give Negative eventhought I would be Positive?  

Thank you
239123 tn?1267651214
Re-read the first paragraph of my original response.

Avatar universal
Hey Doc:

I re-read your first paragraph. And my understanding of what you wrote in the second paragraph is that you are "assuming" that the chance of having a false negative at 6 months is 1%.

I just want to confirm that my understanding is correct.

239123 tn?1267651214
In my initial response, I charachterized the risk as "Certainly no more than 1 chance in 100, probably less than 1 in 1000."  Isn't is obvious that in the next paragraph I chose the higher estimate just to maximize your reassurance in my mathematical example???  If I used the better estimate of 1 in 1000, the calculation of your chance of having HIV becomes 1 in a billion instead of 1 in 100 million.  Don't you understand that this is truly equivalent to zero????

THERE IS NO CHANCE IN THE UNIVERSE THAT YOU HAVE HIV.  Let it go.  If you cannot, you need to seek care from a mental health professional, which I suggest out of compassion, not criticism.

This is my last comment on this thread.

Avatar universal
yes, I do understand 1/100 is 1%! my 3% was referring to the alleged 3-months estimate

well if it indeed is 'only' 1% at 6 months and if a standard heterosexual risk with an unknown person is around 1 in 1,000,000 then we can get to 1 in 100,000,000 with a negative result at 6 months

if it is 3% at 3 months then with the 1 in 1,000,000 risk we are getting to 1 in 30,000,000 at 3 months - some may draw a conclusion that they might as well give up on a test at 3 and 6 months since the odds of still having it 'do not decrease too much' (factors of 100 and 30) as compared to the stress of testing, the risk of false positive etc.....

my point was that surely the tests must be picking up more than 97% at 3 months, given the widspread use of this window period by (conservative) officials and, in some cases 10 year experience with such a practice. my example was an illustration that 97% would be quite unsatisfactory from a public health point of view.

Avatar universal
Thank you for your answer and honesty.
Avatar universal
Didnt answer my question... oh well.  I thought it was valid.  A bit different from the rest?  But alas, Impatience won the day.  I cringe at your tone at times sir... Reminds me of a special ed teacher getting red in the face and telling all the kids to JUST SHUT THE @#*$^ UP!!  Maybe you arent cut out for this gig?  I know its not healthy for us to lurk here... but what about you?  You do alot of good by being stern with some.  But to homogenize that tone for nearly every response??  You can email me with a response at ***@****, as I imagine you will delete this. :)  I am a teacher by the by, and can understand your frustration!  


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