Serosorting may reduce HIV transmission but worsen sexual health

Probably the biggest single problem with the serosorting phenomenon, and the reason health educators are reluctant to promote it as a choice, is that while it may limit HIV transmission, it does nothing to protect people from other sexually transmitted infections (STIs). Indeed, if, because of serosorting, HIV-positive people in particular feel much freer to stop using condoms because they are assured they are less likely to pass on HIV, STIs may become concentrated in the HIV-positive population.

It is certainly the case that HIV-positive men have extremely high rates of some (but not all) STIs and, in a couple of cases, form the vast majority of people with infection.

In a German paper already cited,¹ amongst HIV-positive men STI rates were actually higher in men who used serosorting as a strategy than in men who used no sexual harm-reduction strategy at all. Those who serosorted were 4.3 times more likely to have a bacterial STI (gonorrhoea, chlamydia or syphilis) than those who used condoms and/or monogamy as their strategy, whereas those who used no strategy at all were ‘only’ 3.7 times more likely to have an STI than condom users (14% less likely than serosorters). Men who used the ‘bit of both’ strategy of combining inconsistent condom use with serosorting attempts had 2.2 times the risk of an STI than consistent condom users, or half the risk of pure serosorters.

All these figures were adjusted for the number of partners in the last year and so were not due to serosorters having more partners per se. This may, therefore, suggest that serosorting in itself increases the risk of STI infection as a result of UAI being restricted to a smaller pool of people.

When it came to HIV-negative men, only those who had no strategy at all had a raised risk of STIs – 2.1 times the risk more than condom users of monogamous men. However, only a very small number (3%) of negative men were pure serosorters, i.e. reserving unprotected sex solely to partners who were HIV-negative.

Certain STIs are particularly concentrated among gay men with HIV. In 2007, researchers from London undertook a review² of published reports between 1996 and 2006 from twelve European countries (Belgium, Denmark, France, Germany, Ireland, Italy, Netherlands, Norway, Spain, Sweden, Switzerland and the United Kingdom), concerning gay men acquiring four STIs: gonorrhoea; syphilis; lymphogranuloma venereum (LGV); and sexually transmitted hepatitis C.

While HIV prevalence among gay men ranged from 6 to 18% in the countries and cities studied, with a very rough average of 10% infected, the prevalence of HIV in those diagnosed with the four STIs was much greater. The study showed that for:

• syphilis - an average of 42% of men with syphilis had HIV
• LGV - an average of 75% of men with LGV had HIV
• gonorrhoea - rates varied by region, but the incidence was from two to six times higher in HIV-positive than in HIV-negative men
• hepatitis C - almost all cases were amongst men with HIV.

In their discussion of the reasons for the increase in STIs amongst HIV-positive gay men, the researchers point towards improved survival in the HAART (highly active antiretroviral therapy) era, harm-reduction strategies such as serosorting, and sexual networks facilitated by the internet.

Why are LGV and hepatitis C seen almost exclusively in gay HIV-positive men, whereas gonorrhoea and syphilis are not? The researchers suggest several reasons: differences in transmission probabilities and epidemiological synergies with HIV; time since the introduction of STIs into sexual networks; differential sexual behaviours; differences in testing and case finding; and the differential impact of public health interventions.

In other words, we may be seeing a combination of factors including serosorting, the failure to target health messages, biological vulnerability and behavioural differences, all of which are combining to turn HIV-positive gay men into a group with particularly poor sexual health.

Taken together, they note, “the epidemiologic and behavioural data highlight a role for ‘positive prevention’ - i.e. prevention that focuses on the sexual health of HIV-positive gay men in ‘high-risk’ sexual networks as well as on the transmission of STIs and HIV to uninfected MSM.”

They suggest that safer-sex messages should focus on more than HIV prevention and also highlight the consequences of sexually transmitted infection.