Sexually Transmitted Infections and First Sexual Intercourse Age in Adolescents: The Nationwide Retrospective Cross-Sectional Study

Introduction: Sexually transmitted infections (STIs) are major causes of medical and psychological problems globally, while adolescents in South Korea have recently shown rapid changes in sexual behaviors. Aims: We aimed to examine the association between the age of first sexual intercourse and the experience of STIs among adolescents. Additionally, in which specific time period would more likely to get infected from sexual intercourse. Methods: We used data from the 2007-2013 Korea Youth Risk Behavior Web-based Survey. Only adolescents with sexual intercourse experience (N=22,381) were included, and multiple logistic regression analysis was performed. Main Outcome Measures: One dichotomized measure and one continuous measure were assessed: (i) STIs experience (defined as having had STIs); and (ii) association between STIs experience and absolute age gap (defined as temporal differences between secondary sexual character emergence age and first sexual intercourse age). Results: Approximately 7.4% of boys and 7.5% of girls reported had STI. For both boys and girls, the chance of experiencing STIs increased as the age of first sexual intercourse decreased (boys: before elementary school [age 7 or under]: odds ratio [OR]=10.81, first grade [age 7 or 8]: OR=4.44, second grade [age 8 or 9]: OR=8.90, fourth grade [age 10 or 11]: OR=7.20, ninth grade [age 15 or 16]: OR=2.31; girls: before elementary school: OR=18.09, first grade: OR=7.26, second grade: OR=7.12, fourth grade: OR=8.93, ninth grade: OR=2.74). The association between the absolute age gap and STI experience was examined additionally (boys: OR=0.93, girls: OR=0.87). Conclusions: This study shows that earlier initiation of sexual intercourse increases the odds of experiencing STIs. Also as the age gap gets shorter, the odds of experiencing STIs increase. Our study suggests that it is important to consider the time period of first sexual intercourse and to reinforce a monitoring system along with the development of other preventive strategies.