Countering the rise of syphilis: A role for doxycycline post-exposure prophylaxis?

Abstract

Doxycycline post-exposure prophylaxis (PEP) holds the potential to mitigate increasing rates of syphilis among sexual minority men (SMM) in the US yet has received limited attention. Since evaluation of this intervention in actual populations is not currently feasible, we used agent-based models (ABM) to assess the population-level impact of this strategy. We adapted ABM of HIV and HPV transmission, representing a population of 10,230 SMM in Philadelphia, Pennsylvania, US. Parameter inputs were derived from the literature, and ABM outputs during the pre-intervention period were calibrated to local surveillance data. Intervention scenarios varied doxycycline uptake by 20, 40, 60, 80 and 100%, while assuming continued condom use and syphilis screening and treatment. Under each intervention scenario, we incorporated treatment adherence at the following levels: 0, 20, 40, 60, 80 and 100%. Long-term population impact of prophylactic doxycycline was measured using the cumulative incidence over the 10-year period and the percentage of infections prevented attributable to doxycycline at year 10. An uptake scenario of 20% with an adherence level of 80% would reduce the cumulative incidence of infections by 10% over the next decade, translating to 57 fewer cases per 1000 SMM. At year 10, under the same uptake and adherence level, 22% of infections would be prevented due to doxycycline PEP in the instances where condoms were not used or failed. Findings suggest that doxycycline PEP will have a modest impact on syphilis incidence when assuming a reasonable level of uptake and adherence. Doxycycline PEP may be most appropriate as a secondary prevention measure to condoms and enhanced syphilis screening for reducing infections among SMM.

Stellungnahme der Deutschen STI‐Gesellschaft zur antibiotischen STI‐Prophylaxe mit Doxycyclin (Doxy‐PEP, Doxy‐PrEP)

“…In einer Modellierungsstudie wurden verschiedene Szenarien untersucht, um den Einfluss der antibiotischen STI‐Prophylaxe auf die bevölkerungsbezogene Inzidenz der Syphilis zu quantifizieren 28 . Hierfür wurde ein geschlossenes Modell mit einer dynamischen Kohorte von 10 230 Männern, die sexuellen Minderheiten angehören, gewählt (Philadelphia, USA).…”

Position statement of the German STI Society on the prophylactic use of doxycycline to prevent STIs (Doxy‐PEP, Doxy‐PrEP)

“…In a modelling study 28 various scenarios were examined to quantify the impact of antibiotic STI prevention on the population‐based incidence of syphilis. The study used a closed model with a dynamic cohort of 10,230 sexual minority men in Philadelphia, USA.…”

“…The study used a closed model with a dynamic cohort of 10,230 sexual minority men in Philadelphia, USA. Over a period of 10 years, assuming that 20% of MSM and other male members of sexual minorities used post‐exposure STI prevention with doxycycline with an 80% adherence rate, there would be a moderate decrease in syphilis incidence by 10% 28 . It is important to note that the preventive antibiotic intake in the modelling was not stratified by risk behavior; instead, it was applied to all men who belong to sexual minorities.…”

Implementation of STI chemoprophylaxis in the United States

“…Limited modeling studies have suggested significant benefit of STI chemoprophylaxis in reducing syphilis transmission among MSM. 5,14 Data suggest that focusing efforts on MSM and transgender women who are most at risk of STIs (ie, more sex partners, a history of previous STIs) may maximize benefit of STI chemoprophylaxis. Also unknown is whether or not individuals on STI chemoprophylaxis may change their behaviors (ie, increased number of sex partners or less condom use) which could negate some of the protective benefit of the medication ("risk compensation").…”

“…How to maximize benefit and optimize use of STI chemoprophylaxis in populations to achieve these outcomes is unknown. Limited modeling studies have suggested significant benefit of STI chemoprophylaxis in reducing syphilis transmission among MSM 5,14 . Data suggest that focusing efforts on MSM and transgender women who are most at risk of STIs (ie, more sex partners, a history of previous STIs) may maximize benefit of STI chemoprophylaxis.…”