Prevalence and Frequency of Heterosexual Anal Intercourse Among Young People: A Systematic Review and Meta-analysis.

We aim to assess if heterosexual anal intercourse (AI) is commonly practiced and how frequently it is practiced by young people. We searched PubMed for articles published 1975 to July 2014 reporting data on the proportion of young people (mean age <25) practicing heterosexual AI (AI prevalence) and on number of AI acts (AI frequency). Stratified random-effects meta-analysis and meta-regression were used to produce summary estimates and assess the influence of participant and study characteristics on AI prevalence. Eighty-three and thirteen of the 136 included articles reported data on lifetime AI prevalence and monthly AI frequency, respectively. Estimates were heterogenous. Overall summary estimates of lifetime AI prevalence were 22 % (95 % confidence interval 20-24) among sexually active young people, with no statistically significant differences by gender, continent or age. Prevalence increased significantly with confidentiality of interview method and, among males and in Europe, by survey year. Prevalence did not significantly differ by recall period. An estimated 3-24 % of all reported sex acts were AI. Reported heterosexual AI is common but variable among young people worldwide. To fully understand its impact on STI spread, more and better quality data on frequency of unprotected AI, and trends over time are required.