HIVR4P 2016: Anal Sex May Transmit 4 in 10 HIV Infections Among High-Risk U.S. Women

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A study presented at the HIV Research for Prevention conference this week in Chicago suggests that among women at high risk for HIV infection, 40% or more infections might be transmitted via anal intercourse. Because HIV is transmitted, according to different estimates, from 2 to 18 times more easily via anal than vaginal sex (the Centers for Disease Control and Prevention's estimate is 12 times), anal intercourse could be a major -- or even predominant -- contributor to HIV infections in heterosexual women, even if anal sex accounts for only 5%-10% of all sex.

[Produced in collaboration with aidsmap.com]

Jocelyn Elmesfrom Imperial College London and colleagues contacted and surveyed 9304 "high risk" HIV-negative, non-drug-injecting women aged 18-60 who had taken part in the 2010/2013 National HIV Behavioral Surveillance survey.

The researchers determined the proportion who had had anal sex during the last year and the proportion who had anal sex the last time they had sex. Because previous studies have established a link between low income and high HIV risk, the definition of "high risk" was that they had low incomes and lived in one of the 20 highest-prevalence metropolitan areas in the U.S.

The average age of the women was 36.8 years, and 73% of them were black or African American. Nearly a quarter (22%) had had sex in exchange for money, goods, or shelter in the last year.

The survey found that 32% had had anal sex in the last year and 27% had had anal sex the last time they had sex. There was some increase in reporting of anal sex with age, with 22% of 18-19 year olds having had anal sex at their last sex, and 31% of 40-60 year olds. Women who had transactional sex were twice as likely to have had anal sex during the year than other women and were 27% more likely to have had it at their last sex.

Having anal intercourse was associated with other HIV risk factors: women who had anal sex reported 3 times more sex partners in the last year than women who had only had vaginal sex. They were also 50% more likely to report sex with casual partners.

Of particular concern was the fact that women reported they were 60% less likely to have used condoms the last time they had anal, as opposed to vaginal, sex. Overall, 11% of all condomless sex acts among the whole study sample -- including women who did not have anal sex at all -- were anal sex.

The prevalence of anal sex varied from city to city. A third of women in San Juan, Puerto Rico (34%) and New York City (32%) reported anal sex on the last occasion they had sex, compared with about 15% in New Orleans. The annual rate varied from 43% in New York to 17% in New Orleans -- and a very high 60% in San Juan. The prevalence among young women aged 18-19 varied even more widely, from 6% reporting it anal sex the last year in New Orleans to 57% in San Juan.

The researchers then calculated the proportion of HIV transmissions that might be due to anal sex, taking into account local HIV prevalence, incidence, and proportion of people on treatment. Averaged over the 20 cities it came to 38%, ranging from 20% in Denver to 44% in New York and 48% in San Juan. Because these cities had higher rates of anal intercourse than others, the median contribution of anal sex to transmissions was about 33% -- roughly what it was for Miami.

Thus, over a third of HIV infections among women may be due to anal sex. Among young women under 25, the proportion was slightly lower at 30%, and it was also lower among non-Hispanic white women, at 25%. Among women having transactional sex it was higher, at 43%.

There was considerable statistical uncertainty around these figures, however, given the range of estimates for the transmissibility of HIV via anal sex. This meant that the highest and lowest estimates for the proportion of infections due to anal sex (90% confidence interval) were 15% and 64%. If HIV transmissibility via vaginal sex is roughly the same as it is through being the insertive partner in anal sex -- as some studies estimate -- then transmissibility via anal sex could be at the upper range of that estimate. Among gay men, being the receptive partner in anal sex has 18 times the risk of being the insertive partner.

Another caveat was that women who had injected drugs within the last year were excluded. If they had been included then it would mean that the proportion of HIV infections due to anal sex among women in general would be lower. Also, this study only looked at a specific population of women already known to be at high risk of HIV. Fewer women at lower risk might have anal sex.

Nonetheless, this study shows that a considerable proportion of HIV infections in U.S. women may be transmitted through anal sex. Especially as condom usage in anal sex appears to be lower, safer sex advice needs to start incorporating anal sex in messaging for women and consideration should be given to providing PrEP for women more widely.

10/18/16

Source

J Elmes, K Hess, R Silhol, 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). Chicago, October 17-21, 2016. Abstract OA05.02.