The incidence of syphilis infections has been substantially increasing in gay men in the developed world.
We developed an individual-based mathematical model describing syphilis transmission within a gay male population: we used the model to simulate the expected relative impact of numerous screening and treatment interventions, targeting different at-risk groups with various coverage and frequency rates and follow-up schedules.
The model predicts that increasing the proportion of gay men tested each year would have a relatively modest impact on syphilis incidence. However, increasing the frequency of testing can have a large impact, with the prevalence of syphilis reduced substantially if individuals are tested every 3 months. Targeting frequent screening at gay men who have large numbers of partners or who engage in group sex is a more efficient way of reducing syphilis epidemics. Contact tracing the regular partners of infected individuals is the most efficient intervention and can have a significant epidemiological impact with relatively high coverage rates.
Increasing the frequency of testing and treatment are required to mitigate syphilis epidemics. Notifying and testing partners of infected men should occur where possible but the high rates required to reverse epidemic trends are likely to be infeasible. Contact tracing should be a secondary priority that is coupled with increases in the frequency of testing in the population. Encouraging testing among men not previously tested for syphilis is also recommended.
A mathematical model of syphilis transmission within gay men shows that frequent testing (every 3 months) of highly sexually active men is required to mitigate syphilis epidemics. Supplemental digital content is available in the article.
From the *National Centre in HIV Epidemiology and Clinical Research, The University of New South Wales, Sydney, Australia; and †Sydney Sexual Health Centre, Sydney Hospital, Sydney, NSW, Australia
The authors thank Melanie Middleton, Jeff Jin, Joanne Micallef, and Nasra Higgins for providing data. We thank Courtney Bendall, Janaki Amin, Preeyaporn Srasuebkul, Amy Kwon, Kel Heymer, David Regan, and Mathew Law for the use of their computers to run simulations. We also thank Nicolas Parkhill and Dermot Ryan at ACON and the members of STIGMA for useful discussions.
Supported by the Australian Research Council (DP0771620); The National Centre in HIV Epidemiology and Clinical Research is funded by the Australian Government Department of Health and Ageing, and is affiliated with the Faculty of Medicine, University of New South Wales.
Correspondence: David P. Wilson, PhD, National Centre in HIV Epidemiology and Clinical Research, The University of New South Wales, Level 2, 376 Victoria St, Sydney, NSW 2010, Australia. E-mail: email@example.com.
Received for publication March 15, 2009, and accepted October 8, 2009.
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