28/07/08

Australians told not to follow those wild Swiss

Since the Swiss noted that people who take their meds correctly and don’t have other infections are unlikely to pass on HIV, the public health establishment has been in a tizz over how to react. Predictably enough, Australian researchers have done what epidemiologists with a point to make so often do: — they’ve reached for the models.

Using a “simple mathematical model”, they’ve concluded that if HIV positive people and their HIV negative spouses or partners toss the condoms because they’re on meds, HIV transmission could leap four-fold. The research is published in The Lancet, though only the abstract is available to mortals. Basically, if 10,000 infected people have unprotected sex with an uninfected partner twice a week for 10 years, we can expect 300 new HIV infections. That’s quite a bit of fun for not all that many infections, it seems to me, though fie on me for saying so. Of course if the 10,000 infected people are all having anal sex twice a week for 10 years, you get a lower fun-to-infection ratio; the modellers predict as many as 3,500 infections, apparently because ARVs do less to reduce the amount of virus hanging out in rectal secretions.

The publication follows hard on the heels of a statement by the Australasian Society for HIV Medicine, which says that lower viral load is useful in case your consistently-used condom bursts. The Australians fret that the Swiss have confused people:

“This could add to the complexity of public health messages to positive people and the wider community resulting in confusion around HIV therapy, prevention and infectiousness….Lowered VL equates to reduced infection rate but not zero risk of infection.” So keep using the condoms, they say.

In fact, the Australian statement includes a very useful summary of some of the important issues raised by the Swiss statement: the Swiss conclusions are all based on studies of vaginal rather than anal sex, for example. But it is unnecessarily Nannyish. Most people process complex information about risks and rewards every day of their lives. The life partners of people who take antiretorvirals are among the best placed in the world to understand the consequences of perhaps becoming infected with HIV. Public health professionals don’t need to treat them like idiots. Rather, we should lay out the risks as accurately as we know how, and let people decide for themselves if the rewards of sex without a condom are worth the risk of becoming infected by a partner who is on appropriate and well-monitored treatment. If you are a man with an infected wife, a 215 in 10,000 chance over 10 years may seem worth the risk. If you are woman with an infected husband, we’re talking a 425 in 10,000 chance over 10, still worth a punt to many people. If you’re a gay guy, the odds crash to 3,524 in 10,000, and you may want to hang on to the condoms. But isn’t it for you to decide?

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This post was published on 28/07/08 in Pisani's picks, Science.

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  1. Comment by David Hackney, 29/07/08, 12:16:

    Having sex 10,000 times over ten years works out to twice a week. Isn’t that a low average or do I just think people are having more fun then they are? My guess based solely on anecdotes is more likely 4 to 5 times a week spread over a lifetime. More often when young, less as we age.

    Despite what many young people believe, the desire never dies. The most embarrassing experience of my life came when I pushed open the door to my mother’s nursing home room to discover her having sex. She was 82.

  2. Comment by Daniel Reeders, 29/07/08, 02:02:

    @David Hackney, I think 4-5 times per week is a wild over-estimation. It’s a shame the modelling studies David Wilson has done, on this issue and on rising infection rates in Australia, were not based on actual data about the sexual practice of real people.

    Elizabeth, I wonder if you’ve come across research by Skurnik et al, which showed the danger of taking a myth/reality approach to communicating information, in that people exposed to the messages tend to forget the valence (truth/falsehood) over time and remember as true the messages which provoked the strongest emotional response. For a nice summary, see: http://www.acrwebsite.org/topic.asp?artid=250.

  3. Comment by Leah, 29/07/08, 04:26:

    1-2 times per week frequency is consistent with the findings of the 2006 American Sexual Behavior Survey by the National Opinion Research Center @ the University of Chicago.

    “Among those 18-29 frequency averages about 84 times per year. This then falls off steadily to 63.5 times per year for those in their 40s to 10 times per year for those 70 and older. Among the married the decline is even more striking, dropping from 109 times per annum for those under 30 to 17 times per annum for those 70 and older.”

    David, your mom rocks!

  4. Comment by Tormod, 29/07/08, 10:11:

    It’s nannyish, but unless you are making the point that the impact of their being nannyish will be a defiant lack of condom use, I don’t think it’s unnecessary.

  5. Comment by Kees Rümke, 29/07/08, 02:13:

    Elizabeth Pisani wrote:
    “The research is published in The Lancet, though only the abstract is available to mortals.”
    I am happy to learn I am not a mortal. I can read the full text without subscription.

    To make you immortal too, here is the link:
    http://multimedia.thelancet.com/pdf/press/infectiousness.pdf

    The Swiss proffessor Pietro Vernazza replied:
    HIV-Transmission under HAART – Lancet study rather supports “Swiss Statement” than challenging it !
    http://www.infekt.ch/index.php?artID=1567

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