Data analysis
Statistical analyses were performed using GraphPad Prism (GraphPad Software, USA) and R Studio (R Studio Software, USA). Women were grouped by age to include approximately equal numbers within each group (18–21; 22–25; 26–33 years). We used the Fisher exact test to compare baseline STI prevalence between groups, including age group, contraceptive group (copper-IUD, LNG implant and DMPA-IM) and Chi-Square test for PSA detection (detected/not detected), condom use (yes/no) and site (eThekwini/Tshwane). Kruskal-Wallis test was used to compare weight, height, body mass index and number of sex acts in the past three months. We compared STI incidence over the three-month follow-up period between groups using the Kaplan-Meier method. P-values were adjusted for multiple testing using a Bonferroni correction [