Apr 2, 2008
Hi Dr. Bob: If a person claims to have been HIV tested more than once, at least six months apart and have tested negative, can they be infected and spread the virus?
Response from Dr. Frascino
First, regarding the chances of HIV acquisition from various sexual exposures, I can provide the CDC's published estimates for statistical risk, but these population-based statistics should not be used as "actual risk" for any one specific exposure. (See archival post below about HIV statistics.)
The estimated per-act risk for acquisition of HIV from unprotected receptive oral sex on a partner confirmed to be HIV positive is 1 per 10,000 exposures.
The estimated per-act risk for acquisition of HIV from unprotected insertive penile-vaginal sex with a partner confirmed to be HIV positive is 5 per 10,000 exposures.
Your negative HIV Ag/Ab test approximately 10 weeks after your "indiscretions" is extremely encouraging. The vast majority of HIV-positive folks will have detectable levels of anti-HIV antibodies in their blood within four-six weeks. (Antigen detection can be even sooner.) Your negative HIV test combined with your statistical risk put the odds astronomically in your favor for not having contracted HIV. No doubt you'll need the 3-month test for definitive confirmation, but certainly optimism is warranted at this point. Personally I don't believe you need to wait until June (six months) for your WOO-HOO experience. A negative result at three months is sufficient. Certainly the option to reconfirm your results at six months is always open to you, but I don't feel it's essential in this case.
Good luck. My good-luck karma has already been sent and I remain confident all will turn out "well" for you!
HIV STATISTICS Sep 13, 2007
Ive written to you many times over the past 3 years and youve answered several of my questions. Thank you! What I really need to know now is how accurate are your statistics about oral and anal sex. Is it really 1 per 10,000 for oral and 50 per 10,000 for anal? Im trying to explain to my negative partner exactly what our specific risk is. Neither one of us are math whiz-kids but this seems reasonably straight forward. He could expect to become infected once for every 10,000 blowjobs. Right?
Thanks Dr. Bob
Response from Dr. Frascino
"He could expect to become infected once for every 10,000 blowjobs. Right?"??? Well actually no, that would be a wrong conclusion to draw from those statistics!!! I've covered this topic numerous times in the past, but I know HIV statistics can be a confusing topic. So even though this questions has now become a QTND (question that never dies) with an ATNC (Answer that never changes), I'll try to explain the limitations of these statistics once again.
The statistics I quoted are "estimated per-act risk statistics for acquisition of HIV by various exposure routes" published in a CDC document. These statistics were generated by combining a variety of published reports and did not control for many different potential variables that occur in different populations and among individuals. In other words, these statistics are primarily useful in determining relative risk, but not specific risk or actual risk for any individual. The reason for this is that any specific sexual coupling has a wide variety of variables to take into consideration when attempting to quantify specific HIV-transmission risk. These would include both viral factors, such as viral strain and viral load, as well as host factors, such as immune integrity, concurrent illnesses, circumcised/uncircumcised, genetic susceptibility, etc. Add to this nonspecific factors/extenuating circumstances, such as roughness of the encounter possibly causing trauma to mucous membranes, menstruation, etc., and perhaps you will begin to see the difficulty in providing transmission-risk statistics for any specific coupling. Also I should point out we cannot conduct prospective controlled epidemiological studies to try to account for theses variables, as that would be unethical. There are some published reports that address risk associated with specific sexual practices that control for some variables, but these studies usually have relatively small sample sizes and again are not applicable to everyone's specific situation. Another reference that I quote frequently is http://hivinsite.ucsf.edu/InSite?page=kb-07-02-02 (SAFER SEX METHODS). If you review the specific epidemiologic studies in this well referenced report, you'll get a better understanding of the complexity involved in these issues.
So why do I quote the statistics that I do? Good question! The main reason is that I am constantly barraged by anxious wrecks desperately trying to quantify their risk. I use the CDC statistics, because CDC is a very conservative organization and the numbers they generated are an amalgamation of many studies. They also standardized the relative risk to a common denominator ("10,000 exposures to an infected source"), which allows us to discuss relative risk. For instance, unprotected receptive anal sex is approximately 10 times more risky than unprotected insertive penile-vaginal sex, which in turn is approximately 10 times more risky than unprotected insertive oral sex.
I hope that this will help clarify the limitations of these estimated HIV-transmission risk statistics.
The bottom line is really much more concrete and easy to comprehend. If someone has placed himself or herself at risk for HIV, he or she should be HIV tested. Period. End of story.
I can just about hear all the paranoid panicky worried wells beginning to type away furiously, providing me with a blow-by-blow of their latest blow-by-blow and begging for me to quantify their specific risk. But unfortunately, unless the other person they were having sex with was me, I will not have enough specific detail to give them an accurate response. Hell, even if it were me, I still might not be able to give a completely accurate risk quantification!
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