Receptive anal sex contributes substantially to heterosexually acquired HIV infections among at-risk women in twenty US cities: Results from a modelling analysis.

PROBLEM: Receptive anal intercourse (RAI) is more efficient than receptive vaginal intercourse (RVI) at transmitting HIV, but its contribution to heterosexually acquired HIV infections among at-risk women in the USA is unclear. METHOD OF STUDY: We analysed sexual behaviour data from surveys of 9152 low-income heterosexual women living in 20 cities with high rates of HIV conducted in 2010 and 2013 as part of US National HIV Behavioral Surveillance. We estimated RAI prevalence (past-year RAI) and RAI fraction (fraction of all sex acts (RVI and RAI) at the last sexual episode that were RAI among those reporting past-year RAI) overall and by key demographic characteristics. These results and HIV incidence were used to calibrate a risk equation model to estimate the population attributable fraction of new HIV infections due to RAI (PAFRAI ) accounting for uncertainty in parameter assumptions. RESULTS: Receptive anal intercourse prevalence (overall: 32%, city range: 19%-60%) and RAI fraction (overall: 27%, city range: 18%-34%) were high overall and across cities, and positively associated with exchange sex. RAI accounted for an estimated 41% (uncertainty range: 18%-55%) of new infections overall (city range: 21%-57%). Variability in PAFRAI estimates was most influenced by uncertainty in the estimate of the per-act increased risk of RAI relative to RVI and the number of sex acts. CONCLUSION: Receptive anal intercourse may contribute disproportionately to new heterosexually acquired HIV infections among at-risk low-income women in the USA, meaning that tools to prevent HIV transmission during RAI are warranted. The number of RVI and RAI acts should also be collected to monitor heterosexually acquired HIV infections.