Doxycycline Postexposure Prophylaxis May Dramatically Reduce Syphilis Among Gay, Bisexual, and Other Men Who Have Sex With Men: A Modeling Study.

BACKGROUND

Syphilis cases in the United States have surged over the past decade, and cases are highest among gay, bisexual, and other men who have sex with men (GBMSM). The Centers for Disease Control and Prevention recommends doxycycline postexposure prophylaxis (doxy PEP) for GBMSM recently diagnosed with bacterial sexually transmitted infections to mitigate this burden. Potential drawbacks include increased antimicrobial resistance and microbiome disruption. Here, we estimate doxy PEP coverage levels required to eliminate sustained community transmission among GBMSM while balancing the drawbacks of doxy PEP.

METHODS

We fit a modified susceptible-infectious-susceptible model of syphilis transmission among GBMSM to syphilis case counts by sex-of-sex-partner. We simulated a range of doxy PEP coverage and adherence levels among GBMSM linked to human immunodeficiency virus treatment and prevention over a 10-year period. We tracked syphilis prevalence and incident cases among GBMSM with and without healthcare access.

RESULTS

With a lower bound efficacy estimate (41%) and 10% doxy PEP utilization (coverage × adherence) among GBMSM linked to human immunodeficiency virus treatment and prevention, we estimated a 24% (interquartile range: 17%-30%) reduction in annual syphilis cases among GBMSM over the next 10 years. Under upper-bound efficacy estimates (97%) and 50% utilization, we estimated a 99% (interquartile range: 88%-100%) reduction in annual syphilis cases among GBMSM over the next 10 years. Our model shows that if subpopulations of GBMSM have reduced access to healthcare, then the elimination of sustained community transmission is unlikely over the next decade.

CONCLUSIONS

Doxy PEP may dramatically reduce syphilis incidence among GBMSM, but barriers to healthcare may impede the elimination of sustained community transmission of syphilis.