Improving the Cost-efficiency of Preventive Chemotherapy : Impact of New Diagnostics on Stopping Decisions for Control of Schistosomiasis

Coffeng, Luc E and Graham, Matthew and Browning, Raiha and Kura, Klodeta and Diggle, Peter J and Denwood, Matthew and Medley, Graham F and Anderson, Roy M and de Vlas, Sake J (2024) Improving the Cost-efficiency of Preventive Chemotherapy : Impact of New Diagnostics on Stopping Decisions for Control of Schistosomiasis. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America, 78 (Suppl.). S153-S159. ISSN 1058-4838

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Abstract

BackgroundControl of schistosomiasis (SCH) relies on the regular distribution of preventive chemotherapy (PC) over many years. For the sake of sustainable SCH 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. However, the limited sensitivity of the currently used diagnostic (Kato-Katz [KK]) to detect low-intensity infections is a concern. Therefore, the use of new, more sensitive, molecular diagnostics has been proposed.MethodsThrough 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.ResultsWe found that KK-based strategies perform reasonably well for determining when to stop PC at a local scale. Use of more sensitive diagnostics leads to a marginally improved health impact (person-years lived with heavy infection) and comes at a cost of continuing PC for longer (up to around 3 years), unless the decision threshold for stopping PC is adapted upward. However, if this threshold is set too high, PC may be stopped prematurely, resulting in a rebound of infection levels and disease burden (+45% person-years of heavy infection).ConclusionsWe 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.