Indirect effects of doxyPEP implementation reveal core-group dynamics of bacterial sexually-transmitted infections

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Abstract
Epidemiological theory holds that core groups of high-risk individuals sustain pathogen transmission. However, the scale at which these dynamics operate is poorly understood. We leveraged doxycycline post-exposure prophylaxis (doxyPEP) implementation among at-risk men who have sex with men (MSM) and transgender women (TGW) as a natural experiment to probe bacterial sexually transmitted infection (STI) dynamics within and across sexual networks. DoxyPEP uptake by 9% of at-risk MSM and TGW was associated with pronounced indirect protection within their sexual networks, substantiating the notion that core groups of individuals wield outsize influence on transmission. Risk of chlamydia and syphilis declined by 80% (95% confidence interval: 71-86%) and 65% (30-82%), respectively, among doxyPEP recipients, and by 41% (32-48%) and 29% (13-42%), respectively, among MSM and TGW who did not receive doxyPEP. However, this substantial reduction in disease among at-risk MSM and TGW did not impact incidence among females and other males. Our findings substantiate core group dynamics of STIs among MSM and TGW but call into question the "bisexual bridge" hypothesis positioning this population as a core group impacting STI dynamics among heterosexuals. These findings should inform rational expectations for the impacts of doxyPEP in settings implementing this intervention.
Funding Information
  • US Centers for Disease Control & Prevention (CDC-RFA-FT-23–0069)

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