Using system dynamics modelling to estimate the costs of relaxing health system constraints: a case study of tuberculosis prevention and control interventions in South Africa

Abstract

Health system constraints are increasingly recognised as an important addition to model-based analyses of disease control interventions, as they affect achievable impact and scale. Enabling activities implemented alongside interventions to relax constraints and reach the intended coverage may incur additional costs, which should be considered in priority setting decisions. We explore the use of group model building, a participatory system dynamics modelling technique, for eliciting information from key stakeholders on the constraints that apply to tuberculosis infection prevention and control processes within primary healthcare clinics in South Africa. This information was used to design feasible interventions, including the necessary enablers to relax existing constraints. Intervention and enabler costs were then calculated at two clinics in KwaZulu-Natal using input prices and quantities from the published literature and local suppliers. Among the proposed interventions, the most inexpensive were retrofitting buildings to improve ventilation (US$ 1,644 per year), followed by maximising the use of community sites for medication collection among stable patients on antiretroviral therapy (US$ 3,753) and introducing appointments systems to reduce crowding (US$ 9,302). Enablers identified included enhanced staff training, supervision and patient engagement activities to support behaviour change and local ownership. Several of the enablers identified by the stakeholders, such as obtaining building permissions or improving information flows between levels of the health systems, were not amenable to costing. Despite this limitation, an approach to costing rooted in system dynamics modelling can be successfully applied in economic evaluations to more accurately estimate the ‘real world’ opportunity cost of intervention options. Further empirical research applying this approach to different intervention types (e.g. new preventive technologies or diagnostics) may identify interventions that are not cost-effective in specific contexts based on the size of the required investment in enablers.

Direct estimates of absolute ventilation and estimated Mycobacterium tuberculosis transmission risk in clinics in South Africa

“…These interventions are highly cost effective [50]. This work considers the infrastructural, organisational, and behavioural changes needed for such interventions to be sustainable [50]. These results support additional investment in a package of IPC interventions to limit the transmission of Mtb and other airborne pathogens.…”

“…As part of the wider Umoya omuhle project, we have modelled the impact of TB IPC interventions implemented in clinics, including improvements in natural ventilation, on Mtb transmission both within clinics [48] and in surrounding communities [49]. These interventions are highly cost effective [50]. This work considers the infrastructural, organisational, and behavioural changes needed for such interventions to be sustainable [50].…”

Cost-effectiveness of tuberculosis infection prevention and control interventions in South African clinics: a model-based economic evaluation informed by complexity science methods

“… 12 While some of the strategic level enablers to address these constraints may not be easily quantified for inclusion in the economic evaluation, this information can still be considered as additional evidence alongside the ICERs for prioritising interventions within the proposed TB IPC package. 23 …”

“…A full description of the interventions and enablers cost model, alongside an explanation of how SDM results were used to inform the costing exercise, is published elsewhere. 23 Interventions were designed and costed based on the characteristics of the two clinics in the area where the social contacts survey was conducted. Clinic 1 is a large periurban facility, while clinic 2 is a smaller rural facility in a relatively less affluent area.…”

“…Annual costs of core intervention activities and enablers were estimated from a provider perspective by combining price and quantity data from the published literature and local supplier quotes. A full description of the interventions and enablers cost model, alongside an explanation of how SDM results were used to inform the costing exercise, is published elsewhere 23. Interventions were designed and costed based on the characteristics of the two clinics in the area where the social contacts survey was conducted.…”