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Medical HIV question: risk of infection

  1. Jul 4, 2011 #1
    One website gives the risk of infection by HIV for a woman during unprotected vaginal intercourse with an infected male partner as "between 1/1000 and 1/100,000." The CDC estimated the number of undiagnosed persons in the greater U.S. with HIV in 2009 at a conference as 230,000. Using a very rough estimate of the number of males over the age of 18 in the U.S. (150 M--it is of course smaller), one might give a ballpark estimate of the risk of unprotected sex (per event) for a woman as [using 1/1000 times 230,000/150M] about 2/million.

    Finding the annual risk for such behavior, with the many simplifications above, one could calculate Probability(one or more encounters that lead to infection) as 1-Probability(no infectious encounters). The probability of no infectious encounters is
    ----
    N = (1 - 2/1000000)^365.
    ----
    The probability of at least one adverse event in a year is then 1 - N = 0.00073 or roughly 7/10,000. I notice that one non-scholarly article gives the annual probability of being murdered as about 1/16,500.

    I don't think statistics help much in this area, but as a back-of-envelope calculation, it seems low. Can anyone suggest a factor that would change the order of magnitude of the risk? Thanks.
     
    Last edited by a moderator: Jul 13, 2011
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  3. Jul 4, 2011 #2

    Evo

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    Re: HIV question

    Please post the links to the studies to which you are referring. We only accept mainstream science and acceptable peer reviewed journals as sources. Anything else is anecdotal and we can't work with anecdotes.

    Once we are all on the same page we will be able to discuss.
     
  4. Jul 4, 2011 #3
    Re: HIV question

    http://aids.about.com/od/hivaidsstats/f/infectionrisk.htm. The content of this site is checked and approved by, among 12 other licensed MDs, Meredith Shur, M.D., of Sinai Hospital, NYC, whose specialty is OB-GYN. This is the source of my risk number (between 1/1000 and 1/100,000). The credentials of the doctors on the review board make it clear it is mainstream.

    http://www.cdc.gov/hiv/resources/factsheets/us.htm [Broken]. This is the CDC's fact site, in which they estimate that 1M people are living with AIDS in the US, of whom 21% are unaware of the infection. The CDC is also a mainstream source.
     
    Last edited by a moderator: May 5, 2017
  5. Jul 4, 2011 #4
    Re: HIV question

    http://www.cdc.gov/nchs/data/dvs/LCWK10_2005.pdf gives the homicide statistic, which is ancillary to the question but given for perspective. Out of 2,448,017 deaths in 2005, 8770 were due to homicide, which is about 0.00358. So about 36/10000. Again the source is CDC's site. In my post I may have used a figure from another year.
     
    Last edited: Jul 5, 2011
  6. Jul 6, 2011 #5
    Re: HIV question

    Some of the simplifications I used: 1) all undiagnosed infections [230,000 in the OP, 210,000 per the CDC site] are men--this gives an overestimate; 2) the use of 1/1000 is the highest risk in the cited forum, so would give a higher risk; 3) the exponent 365 raises the risk--I doubt anyone actually incurs this much risk; the estimate of number of men over 18 is high. This tends to dilute the risk but the preceding factors would seem to compensate.
     
  7. Jul 6, 2011 #6

    Ygggdrasil

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    Re: HIV question

    There is one factor that could be hard to model, which is that the sexual promiscuity of the men in the population is not homogeneous. That is, some men in the population will have very few partners while some men will have very many partners. Since the most promiscuous individuals are both the most likely to be sexual partners and are at highest risk for HIV infection, this heterogeneity in promiscuity would tend to elevate the risk from calculations where promiscuity is assumed to be homogeneous.
     
  8. Jul 6, 2011 #7
    Re: HIV question

    That's an interesting point. A 'randomly selected partner' is really a fiction.
     
  9. Jul 7, 2011 #8
    Re: HIV question

    Also, the annual probability of death by (say) homicide assumes one is going to die in a given year, and that probability [from actuarial tables] must be accounted for. It would lower the number and perhaps put it in line with the number [1/16,500] in OP. An interesting coincidence--*death* by homicide and HIV both contribute 0.5 % to the annual deaths for 2005. So we know without further calculation that the probability of *contracting* HIV is much higher (annually) than of dying by homicide.
     
  10. Jul 7, 2011 #9

    enigma

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    Re: HIV question

    Unprotected vaginal intercourse isn't the only way a woman can contract HIV.

    Intravenous drug use and other types of sex are just two of several possibilities.
     
  11. Jul 7, 2011 #10
    Re: HIV question

    ________________________________________

    True, but the HIV risk cited (1/1000) speaks to vaginal sex. The origin of the undiagnosed cases is not specified. So I don't think this affects the probabilities calculated. If we threw in other types of sex, it would perhaps affect the calculation, but I wonder whether there is a research incentive to find HIV infection risk for sexual encounters of an unspecified nature.
     
    Last edited: Jul 7, 2011
  12. Jul 9, 2011 #11
    Re: HIV question

    receptive anal intercourse is the easiest way to get it. this is not rare heterosexual behavior. i suspect it is also not rare for some bisexual (situational or otherwise - note the category is called MSM) men to not inform female partners of past encounters. some are also never going to admit to healthcare providers how they contracted a disease. some may barely be able to admit it to themselves. and... a lot of unwise sexual choices happen under the influence of drugs and alcohol. some may literally have no idea of what happened.

    as for teasing out info from reluctant people, there is an indirect method from psychology that uses a little statistical trick, but i can't remember what it's called.
     
  13. Jul 10, 2011 #12
    Re: HIV question

    ____________
    Agreed, especially about the difficulty of getting data. So if I understand you correctly, instead of focusing on the "randomly selected partner," who as Ygggdrasil suggested may be drawn from a smaller pool than we imagined, you are saying that the risk appears small with vaginal intercourse because it is only a component of a greater overall risk. I think this is a good answer, although I do think it's important to assess each component. To the extent people are sober, relative risk is still something to be weighed.
     
  14. Jul 13, 2011 #13
    Re: HIV question

    nice very unique post i don't thing before this i saw any this type of comparison about the HIV.
     
  15. Jul 13, 2011 #14

    Ygggdrasil

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    Re: HIV question

    For what it's worth, the CDC estimates that the yearly incidence of new infections per year in the US is 56,300, 31% of which are due to heterosexual contact (http://www.cdc.gov/hiv/topics/surveillance/incidence.htm [Broken]). If we can get an estimate of the number of sexually active heterosexual individuals in the population, we can compare daniel6874's back-of-the-envelope risk estimate to the actual incidence rate.
     
    Last edited by a moderator: May 5, 2017
  16. Jul 14, 2011 #15
    Re: HIV question

    Sort of agreed, but I think the earlier observation that needle-sharing and anal sex potentially dwarf the contribution of vaginal intercourse (for women, obviously) make it a hard call. Assuming some continuity of figures year over year, if 20,000 (men and women) are newly HIV+ (roughly your figure), we would need about 28.5 million active heterosexuals (men and women, and we would include bisexuals) to get a similar risk (for both men and women).

    There may be this many. It's about 10% of the population.
     
    Last edited by a moderator: May 5, 2017
  17. Jul 14, 2011 #16

    Evo

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    Re: HIV question

    Injection drug users come in third.

    http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5846a2.htm
     
  18. Jul 14, 2011 #17
    Yes, and I missed that the infections in Ygggdrasil's statistic are already due to heterosexual sexual encounters. So I guess the question of how many active heterosexuals there are would give a statistic for comparison, bearing in mind the comparison is between annual risk for the general heterosexual population and that for women alone due to vaginal intercourse (the OP), just to check that the risks are of the same order of magnitude. If there are studies estimating that number, I'd be interested.
     
  19. Jul 14, 2011 #18

    Evo

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    What exactly are you looking for? Just numbers? And why?

    Risk of infection has to do with the risky behaviour you or people you are involved with take.

    A gay or heterosexual couple that are monogamous, not infected and not used syringe injection drug users or partners of same, are virtually at no risk, (except for the rare chance that they get a contaminated blood transfusion, etc...)
     
    Last edited: Jul 14, 2011
  20. Jul 14, 2011 #19
    The question is in the OP. The CDC published the numbers. I respectfully do not understand your question(s).
     
  21. Jul 14, 2011 #20

    Evo

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    If this is your question (it's the only one I see), it's too vague. You need to be specific, if you could answer my questions, that would help.

    Which risk? Sharing needles with injected drug users? Having sex with these users? Having sex with already infected partners?

    I explained in my post above how you can choose to be in an extremely low risk group.

    Perhaps this will help.

    http://www.cdc.gov/hiv/topics/surveillance/resources/reports/
     
    Last edited: Jul 14, 2011
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