April 3, 2012
Some seroadaptive behaviors appear to be even more effective than 100% condom use at reducing the risk of HIV acquisition, but with important caveats, according to a paper presented last month at the 19th Conference on Retroviruses and Opportunistic Infections (CROI 2012).
Researchers from San Francisco and Seattle, led by Snigdha Vallabhaneni, M.D., analyzed data from four previous HIV prevention studies. Data was collected on 12,705 HIV-uninfected men who have sex with men (MSM) from North America, with sexual behavior self-reports and HIV testing conducted every six months for 18 to 36 months. Among the study population, 663 ended up contracting HIV.
On each visit, the participants were categorized into one of six categories:
The categories were mutually exclusive and hierarchical: If the participants did practice the first option, they were placed into that category. If not, they were asked about the second option, and so on until they were found to have practiced one of the options. If they didn't practice any of the first five options, then they were placed in the sixth category, "no seroadaptive practices."
Of the six categories, options two through five were referred to as seroadaptive behaviors.
In terms of the study population, the median age was 34. Seventy-eight percent of the participants were white, 6% were black and 11% Hispanic. The number of sexual partners that the participants had every six months was stratified as 0 to 1, 2 to 5, 6 to 10 and more than 10; a plurality (37%) had between 2 and 5 partners. Meth use was reported in 10% of participants, while 31% used poppers.
Forty-seven percent of the MSM studied were categorized as having no UAI; 21% were categorized as not using any seroadaptive practices; and 32% were categorized as having used a seroadaptive behavior. Specifically, 11% were categorized as having a single, uninfected partner, 10% were exclusive tops, 8% practiced serosorting and 3% practiced seropositioning.
In the analysis, serosorting was found to more than double the relative HIV risk when compared to having no UAI.
Remarkably, when compared to having no UAI, having a single, uninfected partner was found to reduce relative HIV risk by 44%, and being an exclusive top reduced risk by 45%. "We believe that we saw this result because people are likely to over-report condom use," Vallabhaneni told TheBodyPRO.com. "We know that, from other studies, nearly a quarter of infections among MSM can be attributed to insertive anal sex -- so having unprotected, insertive anal sex is not a good strategy. Condom use and limiting the number of partners are the most important strategies one can use."
Vallabhaneni also noted that although the study seemed to find 15% less risk for HIV acquisition among those who used seropositioning (based on an adjusted hazard ratio of 0.85) when compared to the HIV risk among those who used no UAI, the adjusted hazard ratio actually ranges between 0.50 and 1.44, meaning the relative HIV risk of seropositioning is not significantly different than having no UAI.
In the end, seroadaptive behaviors should work in complement with regular condom use and HIV testing, Vallabhaneni suggested. "The main message we would like to get out there is that serosorting itself is twice as risky as not having unprotected anal sex," she said. "But it has a 38% risk reduction when compared to having no strategy at all -- so it may be a harm reduction strategy for those engaging in the highest risk behavior."
Vallabhaneni added that frequent HIV testing was a key component of any harm reduction strategy. "For serosorting to be useful at all, it is important that men get tested regularly (every three to six months for sexually active MSM) to know their own status, and have disclosure conversations so that they know the status of their partners -- instead of guessing about it," she said.
Vallabhaneni noted that this research contributes to a larger project known as the Prevention Umbrella for MSM in the Americas (PUMA), a research study that will look at combination prevention strategies. "We know that no one prevention strategy is effective by itself," she explained. "But the hope is that combined approaches may be more effective. For example, we could combine home testing for HIV and seroadaptive practices to make seroadaptive practices more effective (since their effectiveness depends on knowing your own status and your partner's status)."
"Our team is also planning on doing a similar analysis of a cohort of African-American MSM -- the group currently at highest risk for HIV infection," Vallabhaneni added.
Warren Tong is the research editor for TheBody.com and TheBodyPRO.com.
Follow Warren on Twitter: @WarrenAtTheBody.
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