Abstract
PURPOSE: Adolescent girls and young women (AGYW) are disproportionately affected by STIs. Observation of life course events can describe behavioral and biological factors associated with STI risk. METHODS: Sexually inexperienced AGYW aged 16-20 years in Kenya were followed for five years. Quarterly visits assessed for C. trachomatis (CT), N. gonorrhea (GC), and T. vaginalis (TV), bacterial vaginosis (BV), HSV-2, and HIV. Sexual activity was self-reported but amended if incongruent with results from STI, pregnancy, or any other testing. Cox regression and Generalized Estimating Equation models were used to determine hazard ratios (HRs) and relative risks (RRs) of STI. RESULTS: During follow-up, 293 of 400 participants reported sex, 163 AGYW experienced an STI, and 72 participants had multiple STIs. Among 163 participants that experienced an STI, there were a total of 259 visits where STIs were detected, 78% (n = 201) of which included CT. Cox regression found participants with BV had over two-fold higher risk of first STI acquisition (adjusted hazard ratio (aHR): 2.35; 95% confidence interval (CI) 1.43-3.88; p = .001). Increased risk for first STI episode was associated with a new partner (aHR: 3.16; 95% CI 1.59-6.28; p = .001). AGYW who did not disclose sexual activity had the highest risk (aHR: 3.60; 95% CI 1.93-6.70; p < .001). Condom use was low, with 21% reporting condom use with sex. GEE analysis of all STIs including incident, prevalent, and recurrent, confirmed these risk factors. DISCUSSION: During the critical years after first sex, AGYW with BV, new sexual partners, and those who did not disclose sexual activity were at highest risk for STI events, especially CT.