Background:
Though the prevalence and epidemiology of anal intercourse (AI) are well described among men who have sex with men (MSM), less is known about heterosexual AI.

Objective:
To evaluate the epidemiology and risk factors of STD patients who report AI.

Method:
This cross sectional study used demographic and risk behavior data collected from patients presenting at public STD clinics in Los Angeles. Current infection with an STD was determined using laboratory testing data. New patient visits from May 2006– June, 2007 were included in the analysis.

Result:
Among the 25,613 patients, the mean age was 31 years and 35% were women. Overall, 17% reported AI in the past 90 days. Among men with only female partners (MSW) 11% (1,528/13,422) reported AI and 12% (976/8,131) of women reported AI. Among men reporting sex with women and men (MSM/W) 53% reported insertive AI and 34% receptive AI (n=638). The overall prevalence of chlamydia and gonorrhea among women reporting AI was 13% and 2.4% respectively. Among MSW reporting AI, chlamydia and gonorrhea prevalence was 12% and 4.4%. MSM/W reporting AI had a chlamydia and gonorrhea prevalence of 6.5% and 5.9% respectively. Predictors of AI for heterosexuals included methamphetamine use (OR=3.20; 95% CI: 2.40-4.28), exchanging sex for money/drugs in the past 12 months (OR=2.79; 95% CI: 1.97-3.95) and recent incarceration (OR=1.71; 95% CI: 1.39-2.10). Other predictors were heroin, ecstasy and anonymous sex. For MSW, MSM/W and women, the prevalence of chlamydia and gonorrhea was no different among those who practice AI and those who did not.

Conclusion:
The prevalence of AI was relatively high among this population of STD clinic patients. Though heterosexual patients practicing AI reported riskier behaviors, they were not more likely to have chlamydia or gonorrhea.

Implications:
There is a need for better understanding of the impact of anal intercourse on STD/HIV transmission in different populations.