Serosorting may have contributed to overall declines in HIV incidence in Seattle, according to a study from the University of Washington School of Public Health. Research findings highlighted how the practice, while not ideal from a public health standpoint, represented a significant step toward safer sexual behaviors for some men.

The study found that, between 2001 and 2013, serosorting increased substantially among both HIV-positive and HIV-negative men who have sex with men (MSM) in Seattle. Serosorting is the process by which MSM choose their sex partners or selectively use condoms based on a partner’s perceived HIV status, the study noted.

Synchronous with this change, findings also showed that the proportion of HIV-negative MSM who reported having condomless anal sex with HIV-positive partners or partners of unknown HIV status declined.

“Given that serosorting confers a lower risk of HIV acquisition than having condomless sex with HIV-positive or unknown status partners, this change indicates a shift toward generally safer sexual risk behaviors among HIV-negative MSM,” said lead researcher Christine Khosropour, who conducted the research as a PhD student in the School’s department of epidemiology.

The study, published in the Journal of Acquired Immune Deficiency Syndromes, found that men who practiced serosorting had a 47 percent lower risk of testing HIV positive compared to men who had condomless anal sex with HIV-discordant partners or partners of unknown HIV status. Within the study period, the proportion of all MSM testing newly positive for HIV declined.

Researchers studied nearly 50,000 clinic visits made by MSM over a 12-year period — currently the largest and longest-running study of serosorting trends in the United States. Data was collected as part of routine clinical care from men who visited the Public Health – Seattle & King County STD Clinic at Harborview Medical Center and the Gay City Health Project, a community-based HIV/STI testing center.

MSMs were asked about their sexual behavior, the gender of their sex partners and the frequency of condom use with HIV-positive, HIV-negative and unknown-status partners in the prior 12 months before visiting the centers.

Though the findings were mostly promising, the study also showed a decrease in consistent condom use among HIV-positive MSM. Therefore, the “results lend support to public health messaging that promotes consistent condom use as the best risk reduction strategy,” the study suggested.

“For populations of MSM where HIV testing is common and HIV status disclosure is high, however, serosorting is an effective HIV prevention strategy among MSM for whom consistent condom use is not achievable,” Khosropour said. “For all MSM, coupling behavioral strategies to reduce HIV risk with biomedical strategies to prevent HIV acquisition is likely the most effective HIV prevention strategy.”

Findings also lend some support to the idea that serosorting may increase the risk of STIs other than HIV. According to the report, the increase in serosorting may have contributed to the current syphilis epidemic among HIV-positive MSM in Seattle. However, the study noted, the magnitude of this contribution is uncertain.