The practice of choosing to only engage in unprotected sexual activity with partners of the same HIV serostatus has been viewed by some public health experts as an effective HIV prevention tactic. But a new analysis, employing a mathematical model, suggests that this practice, known as serosorting, may actually be associated with an increased risk of HIV infection, largely due to recently infected individuals still thinking and disclosing that they are seronegative.
As is discussed in an article published in the February/March 2007 issue of POZ, many people living with HIV have based sexual and romantic choices on serostatus since the beginning of the epidemic. In recent years, an official term for this behavior was coined by prevention experts and is frequently used in the scientific literature: serosorting.
Same-status, or seroconcordant, partnering can alleviate pressures around issues like stigma, disclosure, and transmission fears. While serosorting is not uncommon among HIV-positive and HIV-negative individuals seeking out long-term romantic partners, it is also frequently practiced among people seeking out specific sexual activities, such as condomless sex with short-term partners. In fact, the latter concept is now supported by the San Francisco Department of Public Health (SFDPH) as an effective HIV prevention tactic, while other urban health departments, from Seattle to Denver to New York, are currently researching the potential of serosorting to drive down new infections.
SFDPH predicts that new HIV infections among men who have sex with men (MSM) citywide will be about 20% lower in 2006 than in 2001. The department attributes the phenomenon primarily to serosorting, which studies show has been on the rise among MSM in the Bay Area since the late 1990s.
In November, SFDPH began a highly visual print and Web campaign featuring silhouettes of naked men embracing in erotic poses with their HIV status branded on their shoulders, with a caption reading, "Status-Sorting is a Prevention Strategy."
But according to a research letter in the May 31 issue of AIDS by David Butler, MD, and Davey Smith, MD, of the University of California, San Diego, effective serosorting – as a method of preventing HIV transmission, at least among HIV-negative individuals seeking unprotected sexual activity with other HIV-negative individuals – is highly dependent on a key variable. "If other prevention methods, such as latex condoms, are not employed with every sex partner but only with those having a discordant serostatus, then knowing the true HIV status is imperative," they write. "Without lying, some HIV-infected individuals may mistakenly believe they are not infected and disclose as 'HIV negative'."
Because the effectiveness of serosorting depends upon accurate disclosure, Drs. Butler and Smith conducted some mathematical modeling to calculate the risk of transmission from 'HIV-positive' versus 'HIV-negative' disclosers to someone who is not infected and not using condoms. The modeling took into account two, often overlapping, factors that can work against serosorting: undiagnosed infections and infectivity by stage of infection.
Individuals who incorrectly disclose as 'HIV negative' are either chronically or recently infected. Although standard antibody tests diagnose chronic infection with a very low false-negative rate, acute disease – the first several weeks of the infection phase – cannot be diagnosed by standard HIV testing until after detectable antibodies have been produced. Individuals may erroneously believe themselves to be uninfected after a negative antibody test result, or if they haven't had a recent antibody test, and disclose themselves as 'HIV negative' to sexual partners when, in fact, they are highly contagious.
During the period of recent HIV infection, individuals typically have a much higher viral load than they do for most of the time that they are infected, and the viral load has been shown to correlate with infectiousness. During acute infection, which lasts approximately six to eight weeks, infectiousness is probably greater than at any other time. Infectiousness, however, can remain elevated for up to 25 months after infection. .
According to Drs. Butler's and Smith's mathematical model, as the proportion of recently infected potential sex partners in a population increases, the effectiveness of disclosure for preventing HIV transmissions by serosorting decreases. In certain "high-risk" populations and settings, there may be a significant percentage of people who believe they are negative but are instead in the early throes of HIV infection. In turn, HIV-negative individuals may actually face a lower risk of infection upon having unprotected sex with someone who is admittedly positive (and most likely in the chronic stage of infection with a lower viral load), compared to someone who claims to be negative.
"The effectiveness of serosorting on the basis of mutual disclosure of perceived HIV status is a flawed strategy for reducing sexual transmissions of HIV when it does not consider the prevalence of recent HIV infections in specific populations," the authors conclude. "Importantly, the individuals at greatest risk of HIV infection predictably belong to these very groups having the greatest proportions of recently infected people. By ignoring the increased potential for HIV transmission by recently infected individuals, serosorting may paradoxically increase the number of new HIV infections in certain populations."
Source:
Bulter D, Smith D. Serosorting can potentially increase HIV transmissions. AIDS 21(9):1218-20, 2007.
