Modelling Cost-Effectiveness of Syphilis Detection Strategies In Prisoners: Exploratory Exercise In A Chilean Male Prison

Abstract

BACKGROUND: Syphilis, together with other sexually transmitted infections, remains a global public health problem that is far from being controlled. People deprived of liberty are one of the vulnerable population. Control activities in prisons rely mostly on passive case detection, despite the existence of affordable alternatives that would allow switching to active case-finding strategies. Our objective was to develop a mathematical modelling framework for cost-effectiveness evaluation, from a health system perspective, of different approaches using rapid tests for the detection of syphilis in inmates' populations and to explore the results based on a Chilean male prison population. Methods: A compartmental model was developed to characterize the transmission dynamics of syphilis inside a prison with the ongoing strategy (passive case detection, with VRDL + FTA-ABS), considering the entrance and exit of inmates over a 40 year period. The model allows to simulate the implementation of a reverse algorithm for the current situation (rapid test + VDRL), different screening strategies (entry point, massive periodically; both with rapid test + VDRL) and treatment of detected cases. The parameters for the exploratory exercise were obtained from systematic searches of indexed and grey literature and field work (EQ-5D questionnaire application and key actors interviews). Probabilistic sensitivity analysis was conducted to account for uncertainty in relevant parameters. RESULTS: The proposed framework allows the evaluation of different detection strategies. In this study, all the strategies were cost-effective in the baseline scenario when considering an ICER threshold of 1 Chilean GDP per capita (US$15,000). The strategies most likely to be cost-effective (over 80% probability) were: current situation with reverse algorithm, entry point screening and mass screening every two years; the latter was the most effective, achieving the lowest prevalence (0.7% and 1.7% over the period versus the 3% prevalence in the current situation).CONCLUSIONS: Mathematical modelling that considers the performance of different test and detection strategies might be a powerful tool for decision making. The exploratory results show the efficiency of adopting both the use of the rapid tests and to perform active case detection to significantly reduce the burden of syphilis in Chilean prisons in the near future.

Optimal control of diseases in prison populations through screening policies of new inmates

“…In what follows, by Pontryagin extremal (or extremal trajectory) we refer to a tuple (x(•), λ(•), λ 0 ) satisfying ( 3), (11), and ( 12), for some control w(•), with λ 0 ∈ {0, 1} and (λ 0 , λ(•)) not null.…”

“…Let us define λ ncl (•) as the λ−nullcline, which, from (11), has an explicit expression as a function of x:…”

“…Because of this, the World Health Organization (WHO) includes prisoners in the key populations that should be the focus of interventions designed to reduce the burden of diseases [16,26]. Currently, for some diseases, there are proven technological resources that facilitate access to the diagnosis, and subsequent treatment, of communicable diseases in low-resource contexts, such as the existence of low complexity rapid tests, which can be applied by personnel with basic training [4,5,11,17,23,24,27,28]. For STIs, the diagnostic strategies based on rapid tests have the potential to increase access to definitive diagnosis for asymptomatic patients, preventing the development of long-term complications, and cutting the chain of disease transmission in the population [29].…”

“…For STIs, the diagnostic strategies based on rapid tests have the potential to increase access to definitive diagnosis for asymptomatic patients, preventing the development of long-term complications, and cutting the chain of disease transmission in the population [29]. The above notwithstanding, little is known about the use of these technologies in prison contexts, where the most widespread practice for identifying cases is the passive casedetection, mainly based in symptoms, despite the existence of relatively less expensive alternatives that would allow switching to active case-finding strategies [11].…”