Evidence for

Serosorting may be one reason why a large increase in STIs in gay men, especially syphilis, was not accompanied by a similar increase in new HIV diagnoses around the turn of the millennium.1 This shook an assumption previously used by many HIV epidemiologists – that increases in STI rates can be used as surrogate markers or predictors of increases in HIV. This has been found not to be the case.

In 2003, epidemiologists in Seattle and San Francisco noticed that HIV incidence among gay men attending for HIV tests was starting to decline, even though syphilis rates had increased 25-fold.

HIV testing data,2 presented at the 2006 International AIDS Conference in Toronto, showed that the annual incidence of new HIV infections in San Francisco peaked in 1999 at 4% amongst men attending anonymous testing sites and 5% amongst men using confidential HIV testing at sexual health clinics. However, by 2004, HIV incidence amongst gay men in San Francisco had levelled off, to just under 3% a year at these sites.

Audience members in Toronto questioned whether these lower incidence rates might be more due to increased antiretroviral uptake and therefore lower average viral load in HIV-positive gay men.

Subsequent studies in San Francisco3 that estimate incidence amongst the entire gay population of the city have suggested that further declines in HIV incidence in gay men (by about one-third between 2006 and 2008) are associated with better antiretroviral treatment coverage rather than serosorting behaviour. The observed fall in incidence is not as yet statistically significant (p = 0.3) and have so far only shown a correlation between falls in community viral load and HIV incidence, not that one definitely caused the other. See HIV treatment as prevention for more details.

References

  1. Buchacz K et al. Trends in Primary and Secondary Syphilis and HIV Seroincidence among Men Who Have Sex with Men in San Francisco, 1998-2002. 11th Conference on Retroviruses and Opportunistic Infections, San Francisco, abstract 88, 2004
  2. Truong HM et al. HIV serosorting? Increases in sexually transmitted infections and risk behavior without concurrent increase in HIV incidence among men who have sex with men in San Francisco. Sixteenth International AIDS Conference, Toronto, abstract MOAC0105, 2006
  3. Das-Douglas M et al. Decreases in community viral load are associated with a reduction in new HIV diagnoses in San Francisco. 17th Conference on Retroviruses and Opportunistic Infections, San Francisco, abstract 33, 2010
This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.