A model of population dynamics of TB in a prison system and application to South Africa

摘要

BACKGROUND: Tuberculosis (TB) continues to spread in South African prisons in particular, as prisons are over-capacitatedand have poor ventilation. The awaiting trial detainees are not screened on admission and are at high risk ofgetting infected with TB.RESULTS: We propose a compartmental model to describe the population dynamics of TB disease in prisons. Ourmodel considers the inflow of susceptible, exposed and TB infectives into the prison population. Removal of individualsout of the prison population can be either by death or by being released from prison, as compared to a generalpopulation in which removal is only by death. We describe conditions, including non-inflow of infectives into theprison, which will ensure that TB can be eradicated from the prison population. The model is calibrated for the SouthAfrican prison system, by using data in existing literature. The model can be used to make quantitative projectionsof TB prevalence and to measure the effect of interventions. Illustrative simulations in this regard are presented. Themodel can be used for other prison populations too, if data is available to calculate the model parameters.CONCLUSIONS: Various simulations generated with our model serve to illustrate how it can be utilized in making futureprojections of the levels of prevalence of TB, and to quantify the effect of interventions such as screening, treatmentor reduction of transmission parameter values through improved living conditions for inmates. This makes it particularlyuseful as there are various targets set by the World Health Organization and by governments, for reduction ofTB prevalence and ultimately its eradication. Towards eradication of TB from a prison system, the theorem on globalstability of the disease-free state is a useful indicator.