Abstract
Neglected tropical diseases (NTDs) largely impact marginalised communities living in tropical and subtropical regions. Mass drug administration is the leading intervention method for five NTDs; however, it is known that there is lack of access to treatment for some populations and demographic groups. It is also likely that those individuals without access to treatment are excluded from surveillance. It is important to consider the impacts of this on the overall success, and monitoring and evaluation (M & E) of intervention programmes. We use a detailed individual-based model of the infection dynamics of lymphatic filariasis to investigate the impact of excluded, untreated, and therefore unobserved groups on the true versus observed infection dynamics and subsequent intervention success. We simulate surveillance in four groups-the whole population eligible to receive treatment, the whole eligible population with access to treatment, the TAS focus of six- and seven-year-olds, and finally in >20-year-olds. We show that the surveillance group under observation has a significant impact on perceived dynamics. Exclusion to treatment and surveillance negatively impacts the probability of reaching public health goals, though in populations that do reach these goals there are no signals to indicate excluded groups. Increasingly restricted surveillance groups over-estimate the efficacy of MDA. The presence of non-treated groups cannot be inferred when surveillance is only occurring in the group receiving treatment.Author summaryMass drug administration (MDA) is the cornerstone of control for many neglected tropical diseases. As we move towards increasingly ambitious public heath targets, it is critical to investigate ways in which MDA weaknesses can be strengthened. It is known that some individuals systematically choose not to participate in treatment. It is also becoming evident that others systematically do not have access to treatment. What is less clear however, is how access to treatment correlates to inclusion in surveillance efforts, and in turn, how this impacts the monitoring and evaluation of intervention programmes. If individuals with access to treatment are more likely to be included in surveillance efforts, then this implies that those without access to treatment are likewise more likely to be excluded from surveillance. Extending the individual-based lymphatic filariasis model, TRANSFIL, we show that exclusion to treatment and surveillance negatively impacts the probability of reaching public health goals, though in populations that do reach these goals there are no signals to indicate excluded groups. Increasingly restricted surveillance groups over-estimate the efficacy of MDA. The presence of non-treated groups cannot be inferred when surveillance is only occurring in the group receiving treatment.