icon-folder.gif   Conference Reports for NATAP  
  HIV Research for Prevention
October 17-19, 2016
Back grey_arrow_rt.gif
One Third of Women in US Study May Pick Up HIV During Anal Sex
  HIV Research for Prevention (HIVR4P), October 17-19, 2016, Chicago
Mark Mascolini
Anal intercourse could explain 38% of HIV infections in women in 20 US cities, according to results of a large modeling study [1]. Collaborators from the Imperial College London, the CDC, and other centers stressed that these women may not represent all at-risk US women and that their findings rely on certain modeling assumptions.
The researchers noted that receptive anal intercourse raises HIV acquisition risk up to 18 times compared with receptive vaginal sex, thus the contribution of AI to HIV infections may be substantial even if 5-10% of all acts are anal. Yet little is known about the contribution of anal sex to HIV incidence in women. These investigators aimed to describe anal intercourse patterns in low-income at-risk women in 20 US cities and to estimate the impact of anal sex on HIV acquisition.
The analysis relied on 2010 and 2013 National HIV Behavioral Surveillance (NHBS) data from the CDC among US women at the poverty level or with a high school education or less. Eligible women had anal and/or vaginal sex with an opposite-sex partner in the past year and did not inject drugs in the past year. Women lived in 1 of 20 cities with high HIV prevalence.* The researchers combined data from the two NHBS surveys to estimate national and city-specific anal intercourse prevalence in the past year and during the last sex act. A static risk equation model estimated the contribution of anal intercourse to HIV infection. The model adjusted for risk behaviors that may differ between women practicing anal/vaginal sex and only vaginal sex.
The researchers focused on 9304 women, 73% of them non-Hispanic black, 42% between 40 and 60 years old, and 23% reporting exchange sex in the past year. Overall, 32% of women (95% confidence interval [CI] 31% to 33%) reported anal sex in the past year, and that rate ranged from 19% to 60% across the 20 cities. Women who had anal sex did so frequently, with an overall last-sex anal intercourse prevalence of 27% (range 18% to 34% across cities).
Compared with women who had only vaginal sex, those who had anal sex had about 3 times as many sex partners yearly, were 50% more likely to have casual sex partners at last sex (adjusted odds ratio [aOR 1.5, 95% CI 1.3 to 1.6), and were 63% less likely to use a condom at last sex (aOR 0.37, 95% CI 0.32 to 0.42).
Modeling estimated that 38% of HIV infections in these women could be attributed to anal sex (10th to 90th percentiles 18% to 55%). The contribution of anal intercourse to HIV ranged from 20% of infections in Denver to 50% in San Juan, Puerto Rico; with NYC just behind San Juan. The analysis detected a trend toward an increasing contribution of anal sex to HIV infection over time. The researchers noted some uncertainties that could affect these estimates, including number of sex acts and how much anal intercourse increases HIV risk compared with vaginal intercourse.
The investigators concluded that anal intercourse "is common and frequent across the US [and] often occurs without condoms and with casual partners." They stressed the need to encourage condom use among at-risk women during both anal and vaginal sex.
1. Elmes J, Hess K, Silhol R, et al. Meta-analysis and modelling study of anal sex practices and its contribution to HIV incidence among high-risk women across twenty US cities. HIV Research for Prevention (HIVR4P 2016), October 17-19, 2016, Chicago. Abstract OA05.02.
*The cities were New Orleans, Denver, Nassau (NY), Dallas, Atlanta, Seattle, Houston, San Diego, Miami, Los Angeles, Chicago, Boston, Philadelphia, Newark (NJ), Washington, DC, San Francisco, Baltimore, Detroit, New York, and San Juan.