Abstract
BackgroundRegular preventive chemotherapy (PCT) targeting high-risk populations is an effective way to control STH in the short term, but sustainable long-term STH control is expected to require improved access to water, sanitation, and hygiene (WASH). However, experimental studies have not been able to conclusively demonstrate the benefit of WASH in preventing STH (re-)infections. We investigated the impact of WASH on STH infections during and after PCT using mathematical modelling.Methods and findingsWe use the individual-based transmission model WORMSIM to predict the short and long-term impact of WASH on STH transmission in contexts with and without PCT. We distinguish two WASH modalities: sanitation, which reduces individuals’ contributions to environmental contamination; and hygiene, which reduces individuals’ exposure to infection. We simulate the impact of varying levels of uptake and effectiveness of each WASH modality, as well as their combined impact. Clearly, sanitation and hygiene interventions have little observable short-term impact on STH infections levels in the context of PCT. However, in the long term, both are pivotal to sustain control or eliminate infection levels after scaling down or stopping PCT. The impact of hygiene is determined more by the effectiveness of the intervention than its overall uptake, whereas the impact of sanitation depends more directly on the product of uptake and the effectiveness.InterpretationThe impact of WASH interventions on STH transmission highly depends on the worm species, WASH modality, and uptake and effectiveness of the intervention. Also, the impact of WASH is difficult to measure in the context of ongoing PCT programmes. Still, we show a clear added benefit of WASH to sustain the gains made by PCT in the long term, such that PCT may be scaled down or even stopped altogether. To safely stop or scale down PCT, policy for WASH and PCT should be integrated.
Highlights
Over 1 billion people are infected with soil-transmitted helminths (STH) [1], the majority of whom are infected with Ascaris lumbricoides, Trichuris trichiura, and/or hookworm (Necator americanus and Ancyclostoma spp.)
The impact of WASH interventions on STH transmission highly depends on the worm species, WASH modality, and uptake and effectiveness of the intervention
We further show that the impact of WASH interventions on STH transmission highly depends on the worm species, WASH modality, uptake, effectiveness, and pre-control endemicity
Summary
Over 1 billion people are infected with soil-transmitted helminths (STH) [1], the majority of whom are infected with Ascaris lumbricoides (roundworm), Trichuris trichiura (whipworm), and/or hookworm (Necator americanus and Ancyclostoma spp.). STH are transmitted through the ingestion of soil contaminated with egg-containing faeces (roundworm and whipworm) or exposure of skin to free-living larvae (hookworm). Prevalence and intensity of STH infections are strongly inversely correlated with access to and use of improved sources of water, sanitation, and hygiene (WASH) [2,3]. World Health Organization (WHO) guidelines recommend that STH are controlled by preventive chemotherapy (PCT) with albendazole (ALB) or mebendazole (MEB) targeted at school age children (SAC), pre-school age children, and groups at high risk of morbidity such as women of childbearing age. Regular preventive chemotherapy (PCT) targeting high-risk populations is an effective way to control STH in the short term, but sustainable long-term STH control is expected to require improved access to water, sanitation, and hygiene (WASH). We investigated the impact of WASH on STH infections during and after PCT using mathematical modelling
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