Title: Modelling The Effect of Syphilis Screening At The Entry Point in Chilean Prisons

OBJECTIVES:To simulate the current syphilis dynamics in Chilean prisons and evaluate the potential effect on syphilis transmission of entry points screening strategy using point-of-care rapid test. METHODS: A compartmental model was developed to characterize the transmission dynamics of syphilis inside the prison with the ongoing strategy and the way it is affected by the entrance of new inmates over 40 year period. The model also allows to simulate the implementation of an entry point screening strategy and the treatment of the detected cases. The model includes seven compartments or disease stages: susceptible, incubation, primary, secondary, latent, and tertiary stages, and immunity period. The individuals transit from susceptible to infected depending on the transmission rate and the number of sexual partners and then continues the natural history of disease according to the duration of the different stages, the detection rate and the treatment effectiveness. The parameters used were obtain from systematic searches of indexed and grey literature and field observation. RESULTS: In the current situation, with no established program for the search of the infection (only upon spontaneous consultation or as a unexpected finding), less than 30% of the cases are detected and treated once in the latent stage, the prevalence of syphilis reaches about 3%. On the other hand, the implementation of an entry screening program using point-of-care rapid test, assuming 90% coverage, would reduce the prevalence to near 1%. CONCLUSIONS: The present study shows the potential impact of implementing an entry point screening program in the context of a high risk population with limited access to health care, such as prisoners. Considering the low cost and simple application of rapid test, a following step should be to assess the cost effectiveness of strategies based on these test in a hard to reach population.