Cost-effectiveness of comparative survey designs for helminth control programs: post-hoc cost analysis and modelling of the Kenyan national school-based deworming program
Authors: Minnery Mark , Okoyo Collins , Morgan Grace , Wang Andrew , Johnson Olatunji , Fronterre Claudio , Montresor Antonio , Campbell Suzy J. , Mwandawiro Charles , Diggle Peter 
Published: August 2023

Background

Soil-transmitted helminths (STH) and schistosomiasis comprise the most wide-spread NTDs globally. Preventative chemotherapy is a cost-effective approach to controlling morbidity of both diseases, but relies on large scale surveys to determine and revise treatment frequency. Availability of detailed information on survey costs is limited despite recent methodological surveying innovations. We micro-costed a survey of STH and schistosomiasis in Kenya, and linked results to precision estimates of competing survey methods to compare cost-efficiency.

Methods

Costs from a 2017 Kenyan parasitological survey were retrospectively analyzed and extrapolated to explore marginal changes when altering survey size, defined by the number of schools sampled and the number of samples taken per school. Subsequent costs were applied to simulated precision estimates of model-based geostatistical (MBG) and traditional survey designs. Cost-precision was calculated for a range of survey sizes per method. Four traditional survey design scenarios, based around WHO guidelines, were selected to act as reference cases for calculating incremental cost-effectiveness ratios (ICERs) for MBG design.

Findings

MBG designed surveys showed improved cost-precision, particularly if optimizing number of schools against samples per school. MBG was found to be more cost-effective under 87 of 92 comparisons to reference cases. This comprised 14 situations where MBG was both cheaper and more precise, 42 which had cost saving with precision trade off (ICERs; $8,915-$344,932 per percentage precision lost); and 31 more precise with increased cost (ICERs; $426-$147,748 per percentage precision gained). The remaining 5 comparisons represented extremes of MBG simulated site selection, unlikely to be applied in practice.

Interpretation

Efficiency gains are possible for deworming surveys when considering cost alone, such as through minimizing sample or analysis costs. However further efficiency maximization is possible when designing surveys using MBG given its improved precision and ability to optimize the balance between number of schools and sample size per school.

Research in context

Evidence before this study

Soil-transmitted helminths (STH) and schistosomiasis are widespread neglected tropical diseases (NTDs) which require preventative chemotherapy (PC) for morbidity control among school–aged children. A key component of PC for both diseases is the use of large-scale surveys to determine prevalence in order to guide treatment frequency, or in the case of very low prevalence, measure potential resurgence. Given the need for a SAC population estimate, surveys represent a substantial proportion of helminth control program budgets. As prevalence of STH and schistosomiasis reduce globally, there is a need to understand costing components of these surveys to make best use of available resources. Recent innovations based on an increasingly sophisticated existing literature, in survey design using geospatial statistical methods to select survey sites have been shown to deliver more precise results, given the same resources, than traditional design approaches. To date, few studies have reported costs of large scale STH and schistosomiasis studies in sufficient detail to allow cost-effectiveness comparisons of geospatially designed surveys against traditional design approaches using real world data.

Added value of this study

Detailed bottom up costing is provided for a representative survey of STH and schistosomiasis conducted in Kenya in 2017. Results are analyzed and extrapolated to demonstrate how costs differ depending on numbers of schools surveyed and individuals sampled per school. Areas of potential efficiency maximization are highlighted. Costs are coupled with a previous simulation study comparing the precision of traditional and MBG-based design and analysis of the same series of surveys conducted in Kenya. A range of cost-precision estimates are generated and compared to show incremental cost-effectiveness ratios of both traditional and geospatial survey design under varying budget constraints, represented by survey size. The geospatial design is shown, under almost all reference case comparisons to be cost saving, more precise, or both.

Implications of all the available evidence

This study quantifies the potential increased efficiency that can be gained when geospatial methods are used to design and analyse large representative surveys of helminths. This is critical for the future of school-based deworming programs as a greater emphasis is placed on maintaining cost-effectiveness in environments where prevalence and morbidity due to STH and schistosomiasis are reducing.