How STI trends track changes in sexual behaviour, online dating and sexual orientation demographics: an analysis of reported bacterial STI incidence and three social behavioural surveys in the USA (2010-2024).

INTRODUCTION: Bacterial sexually transmitted infections (STIs) in the USA rose substantially in the 2010s and incidence remains high, despite reported declines after the COVID-19 pandemic. We aimed to better understand potential changes that may be contributing to these epidemic trends, particularly new behavioural and demographic patterns in the online dating era since ~2010.

METHODS: We used joinpoint models to examine trends in reported incidence for three notifiable bacterial STIs (ie, chlamydia, gonorrhoea and syphilis) in the USA during 2010-2024, and analysed concurrent changes in sexual behaviour, online dating and sexual orientation demographics using three national datasets (ie, the National Survey of Family Growth, General Social Survey and How Couples Meet and Stay Together).

RESULTS: Reported incidence rates of the three STIs increased during 2010-2019 and declined after circa 2020. Common STI behaviour indicators (eg, partner change rate) did not show changes consistent with the STI trends. In contrast, online dating partnership data suggested higher shares of partnerships formed within the same age group among online daters than offline daters. Analyses of sexual orientation demographics revealed marked increases in the population share self-reported as bisexual, particularly among young adults and females, and identified two candidate groups for further investigation (same-sex males and bisexual females) with group-level partner change metrics correlated with STI incidence rates.

CONCLUSIONS: New partnership patterns among online daters and changing demographics of sexual orientation may have influenced STI trends in the USA during 2010-2024. Research is needed to quantify their impacts on STI epidemics.