Improving the cost efficiency of preventive chemotherapy: impact of new diagnostics on stopping decisions for control of schistosomiasis

Background: Control of several neglected tropical diseases (NTDs), including schistosomiasis, relies on the regular distribution of preventive chemotherapy (PC) over many years. For the sake of sustainable NTD control, a decision must be made at some stage to scale down or stop PC. These stopping decisions are based on population surveys that assess whether infection levels are sufficiently low (typically less than 1%). For schistosomiasis control, concerns have been raised regarding the limited sensitivity of the currently-used diagnostic (Kato-Katz or KK) to detect low intensity infections. The use of new, more sensitive, molecular diagnostics has been proposed. Methods: Through statistical analysis of Schistosoma mansoni egg counts collected from Burundi and a simulation study using an established transmission model for schistosomiasis, we investigated the extent to which more sensitive diagnostics can improve decision making regarding stopping or continuing PC for the control of S. mansoni. Results: We found that KK-based strategies perform reasonably well for determining when to stop PC at a local scale. Use of more sensitive diagnostics only leads to a marginally improved health impact (person-years lived with heavy infection) and comes at a cost of continuing PC for longer, unless the decision threshold for stopping PC is adapted upwards. However, if this threshold is set too high, PC may be stopped prematurely, resulting in a rebound of infection levels. Conclusions: We conclude that the potential value of more sensitive diagnostics lies more in the reduction of survey-related costs than in the direct health impact of improved parasite control. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The research presented in this paper was funded through by the Bill & Melinda Gates Foundation (INV-030046), via the NTD Modelling Consortium. KK and RMA also acknowledge funding from the MRC Centre for Global Infectious Disease Analysis (MR/R015600/1), jointly funded by the UK Medical Research Council (MRC) and the UK Foreign, Commonwealth & Development Office (FCDO), under the MRC/FCDO Concordat agreement and is also part of the EDCTP2 programme supported by the European Union. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes 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 All data produced in the present study are available upon reasonable request to the authors