Cost-effectiveness of comparative survey designs for helminth control programs: post-hoc cost analysis and modelling of the Kenyan national school-based deworming program

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. 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. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The author(s) received no specific funding for this work. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethical approval for all surveys was obtained from the KEMRI's scientific and ethical review committee for the original surveys (SSC Number 206), all surveys involved informed consent. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes This work combines two sections of data. The original simulation data can be found in pre-existing publications. Detailed costing data has been provided as supplementary material as part of this manuscript.