Analysis and individual-based modelling of the tuberculosis epidemiology in Barcelona. The role of age, gender and origin.

Abstract Tuberculosis (TB) has existed for millennia and remains a major global health problem. The best estimate is that there were 1.8 million TB deaths and 10.4 million new TB cases in 2015. It is one of the top 10 causes of death worldwide, ranking above HIV/AIDS as one of the leading causes of death from an infectious disease. In particular, the Ciutat Vella neighbourhood in Barcelona has a tuberculosis incidence which is comparable to the incidence in countries like Sudan. Data provided by the Agencia de Salut Publica de Barcelona has been key to this project. It has enabled us to describe and analyse the tuberculosis transmission patterns in Ciutat Vella. We have characterized the strongest TB transmission channels between collectives (i.e. an immigrant male adult will be most likely infected by another immigrant male adult). The age, gender and origin of the TB sick population in Ciutat Vella have been observed to be relevant variables for the determination of transmission patterns. These findings have allowed us to improve a previous Individual-based Model which is used to simulate the tuberculosis dynamics in Ciutat Vella. The model was implemented in NetLogo, a free and open source simulation tool that incorporates a helpful user-friendly interface. To improve the model, age, gender and origin (native/immigrant) have been introduced as new properties of the individuals. The tuberculosis infection and sickening process have now been simulated taking into account the analysed transmission patterns and sickening probabilities, which differ for each different individual profile. This has allowed to observe simulation results closer to reality. Finally, the distributions of ages, gender and origin for the TB cases in Ciutat Vella have been compared to the ones obtained with the simulations. Similar distributions were observed with a reasonably satisfactory agreement in quantitative terms, but further work is required to increase the quality of such agreement. As conclusions, we have seen that the distribution of ages, gender and origin amongst the TB sick population in Ciutat Vella is far from homogenous. The profile of the individuals has a significant effect on the way the disease is developed and transmitted. Depending on the profile, the risk of becoming infected and the risk of progressing to disease varies greatly and special attention must be brought to those collectives which are most susceptible. Immigrant male adults appear to be the hotspot for TB in Ciutat Vella, accounting for over 50% of the total cases and infecting almost 80% of the times individuals with the same profile. Knowing which are the most susceptible collectives and the transmission patterns will allow to apply optimized and more efficient TB control strategies.