Serosorting May Increase the Risk of HIV Acquisition Among Men Who Have Sex With Men

"Serosorting, the practice of seeking to engage in unprotected anal intercourse with partners of the same HIV status as oneself, has been increasing among men who have sex with men," the authors wrote. Its effectiveness as a risk reduction strategy, however, is unclear, particularly given that it depends on the frequency of HIV testing.

In the current study, the researchers used a mathematical model, informed by detailed behavioral data from a highly studied cohort of MSM, to estimate the relative risk of HIV acquisition associated with serosorting compared with not serosorting.

"We demonstrate that serosorting is unlikely to be highly beneficial in many populations of [MSM], especially where the prevalence of undiagnosed HIV infections is relatively high," the authors wrote. "We find that serosorting is only beneficial in reducing the relative risk of HIV transmission if the prevalence of undiagnosed HIV infections is less than -20 percent and -40 percent, in populations of high (70 percent) and low (20 percent) treatment rates, respectively, even though treatment reduces the absolute risk of HIV transmission.

"Serosorting can be expected to lead to increased risk of HIV acquisition in many settings. In settings with low HIV testing rates, serosorting can more than double the risk of HIV acquisition."

The authors concluded: "Therefore caution should be taken before endorsing the practice of serosorting. It is very important to continue promotion of frequent HIV testing and condom use, particularly among people at high risk."

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