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. summary Compared to Kato-Katz faecal thick smears, model-based analyses suggest that the use of more sensitive tests only marginally changes the impact of decisions to locally stop preventive chemotherapy against schistosomiasis in terms of disease burden (person-years lived with heavy infection).