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Go big or go home: impact of screening coverage on syphilis infection dynamics
  1. Ashleigh Tuite,
  2. David Fisman
  1. Institute of Medical Science and Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
  1. Correspondence to Ashleigh Tuite, Dalla Lana School of Public Health, Room 580, 155 College Street, Toronto, Ontario, Canada M5T 3M7; ashleigh.tuite{at}utoronto.ca

Abstract

Objectives Syphilis outbreaks in urban men who have sex with men (MSM) are an ongoing public health challenge in many high-income countries, despite intensification of efforts to screen and treat at-risk individuals. We sought to understand how population-level coverage of asymptomatic screening impacts the ability to control syphilis transmission.

Methods We developed a risk-structured deterministic compartmental mathematical model of syphilis transmission in a population of sexually active MSM. We assumed a baseline level of treatment of syphilis cases due to seeking medical care in all scenarios. We evaluated the impact of sustained annual population-wide screening coverage ranging from 0% to 90% on syphilis incidence over the short term (20 years) and at endemic equilibrium.

Results The relationship between screening coverage and equilibrium syphilis incidence displayed an inverted U-shape relationship, with peak equilibrium incidence occurring with 20–30% annual screening coverage. Annual screening of 62% of the population was required for local elimination (incidence <1 case per 100 000 population). Results were qualitatively similar in the face of differing programmatic, behavioural and natural history assumptions, although the screening thresholds for local elimination differed. With 6-monthly or 3-monthly screening, the population coverage required to achieve local elimination was reduced to 39% or 23%, respectively.

Conclusions Although screening has the potential to control syphilis outbreaks, suboptimal coverage may paradoxically lead to a higher equilibrium infection incidence than that observed in the absence of intervention. Suboptimal screening programme design should be considered as a possible contributor to unsuccessful syphilis control programmes in the context of the current epidemic.

  • SYPHILIS
  • SCREENING
  • MODELING
  • MATHEMATICAL MODEL
  • CONTROL PROGRAMS

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