LONG-TERM EPIDEMIOLOGIC TRENDS OF STIs PRE- AND POST-PrEP INTRODUCTION: A NATIONAL TIME-SERIES ANALYSIS

Abstract

The introduction of pre-exposure prophylaxis (PrEP) for HIV prevention in 2012 marked a pivotal shift in global sexual health strategies. While PrEP has contributed substantially to reductions in HIV incidence, concurrent increases in bacterial sexually transmitted infections (STIs) have been observed across multiple high-income nations. This study assessed long-term epidemiologic trends in major STIs—Chlamydia trachomatis, Neisseria gonorrhoeae, and Treponema pallidum (primary and secondary syphilis)—in the United States from 2007 through 2022, encompassing both the pre- and post-PrEP eras. The objective was to determine whether national STI trajectories demonstrated significant structural changes following PrEP introduction and to quantify the magnitude and direction of those effects using population-based time-series modeling. Annual national surveillance data were extracted from the Centers for Disease Control and Prevention (CDC) National Notifiable Diseases Surveillance System (NNDSS) and National HIV Surveillance System (NHSS), supplemented by population denominators from the U.S. Census Bureau. Longitudinal incidence trends (per 100,000 population) were analyzed using segmented interrupted time-series (ITS) and autoregressive integrated moving average (ARIMA) models. The intervention point was defined as 2012, the year of FDA approval of daily oral PrEP. The analysis quantified pre- and post-intervention slope changes (β₃) and level shifts (β₂), with robustness checks for autocorrelation and model fit. Sensitivity analyses controlled for diagnostic expansion, reporting completeness, and laboratory modernization. Between 2007 and 2022, chlamydia incidence increased from 347.8 to 527.4 per 100,000 (+51.6%), gonorrhea from 117.3 to 210.5 per 100,000 (+79.4%), and primary and secondary syphilis from 5.5 to 17.6 per 100,000 (+220%). In contrast, new HIV diagnoses declined from 19.1 to 9.4 per 100,000 (–50.8%). Segmented regression detected significant post-2012 slope increases for all bacterial STIs (p < 0.01) and a significant negative slope for HIV (p < 0.01). ARIMA validation confirmed the persistence of these trends independent of serial autocorrelation and diagnostic enhancements. Stratified analyses revealed the steepest STI increases among men aged 25–44 years, overlapping with high PrEP utilization networks. Diagnostic adjustments reduced but did not eliminate the observed post-PrEP acceleration, indicating genuine epidemiologic change rather than reporting artifact. This 16-year national analysis demonstrates a pronounced divergence in U.S. sexual health trends following PrEP introduction.