Screen more or screen more often Using mathematical models to inform syphilis control strategiesReport as inadecuate

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BMC Public Health

, 13:606

Chronic Disease epidemiology


BackgroundSyphilis incidence among men who have sex with men MSM continues to rise despite attempts to increase screening and treatment uptake. We examined the marginal effect of increased frequency versus increased coverage of screening on syphilis incidence in Toronto, Canada.

MethodsWe developed an agent-based, network model of syphilis transmission, representing a core population of 2,000 high-risk MSM. Epidemiological and biological parameters were drawn from regional surveillance data and literature-derived estimates. The pre-intervention period of the model was calibrated using surveillance data to identify 1000 credible simulations per strategy. Evaluated strategies included: annual syphilis screening at baseline coverage, increased screening frequency at baseline coverage, and increased coverage of annual screening. Intervention impact was measured as annual prevalence of detected infectious cases and syphilis incidence per year over 10 years.

ResultsOf the strategies evaluated, increasing the frequency of syphilis screening to every three months was most effective in reducing reported and incident syphilis infections. Increasing the fraction of individuals tested, without increasing test frequency, resulted a smaller decline in incidence, because reductions in infectious syphilis via treatment were counterbalanced by increased incident syphilis among individuals with prior latent syphilis. For an equivalent number of additional tests performed annually, increased test frequency was consistently more effective than improved coverage.

ConclusionsStrategies that focus on higher frequency of testing in smaller fractions of the population were more effective in reducing syphilis incidence in a simulated MSM population. The findings highlight how treatment-induced loss of immunity can create unexpected results in screening-based control strategies.

KeywordsSyphilis Mathematical Modeling Men Who Have Sex With Men Sexually Transmitted Infection Electronic supplementary materialThe online version of this article doi:10.1186-1471-2458-13-606 contains supplementary material, which is available to authorized users.

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Author: Ashleigh R Tuite - David N Fisman - Sharmistha Mishra


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