1. Introduction

Soil-transmitted helminthiasis (STH), namely Ascaris lumbricoides, Trichuris trichiura, and hookworms (Necator americanus and Ancylostoma duodenale), remains a significant public health concern, particularly in low- and middle-income countries (LMICs). These parasites are transmitted by ingestion of eggs from contaminated soil (A. lumbricoides and T. trichiura) or by larval penetration of the skin (hookworms). STH transmission is exacerbated by poor water, sanitation, and hygiene conditions, and limited health education (WASH) [1,2]. Routine mass drug administration (MDA) programs, particularly school-based platforms, have led to substantial reductions in STH infections. Nonetheless, reinfection remains a concern in many endemic countries. Studies have reported reinfection rates of up to 10.4% within 1 year after 5 rounds of MDA [3].

Vulnerable groups for STH infections include preschool and school-aged children, as well as women of reproductive age in rural areas, who experience the highest prevalence and intensity of infections [2,4]. Control efforts primarily rely on preventive chemotherapy with a single dose of albendazole or mebendazole, administered annually or biannually based on community prevalence thresholds [5,6]. Despite these gains, the rapid reinfection underscores the urgent need to integrate WASH with MDA to achieve sustainable interruption of transmission.

Control and eventual elimination of STH is of critical importance due to their substantial impact on public health, education, and economic development. Intestinal helminths contribute to malnutrition, iron-deficiency anaemia, growth retardation, and impaired cognitive development, particularly among school-aged children [1,7]. These health effects result in poor school attendance and academic performance, perpetuating the cycle of poverty in endemic areas. Although MDA programs have significantly reduced prevalence in many endemic countries, reinfection remains a major concern, highlighting the need for more sustainable and comprehensive control strategies.

Integrating WASH interventions offers a more holistic, long-term solution to helminth control. While MDA can reduce infection levels quickly, its effects are often temporary unless accompanied by improvements in living conditions and personal hygiene [8]. WASH infrastructure, including access to clean water and improved sanitation, is vital for interrupting transmission pathways, while health education encourages lasting behavioural change. By reducing reinfection rates, these combined efforts not only protect vulnerable populations but also support progress towards the World Health Organization (WHO) 2030 neglected tropical disease (NTD) elimination targets [6].

Health education plays a complementary role by promoting behaviour change and increasing community awareness of STH prevention. Educating children and caregivers about hand hygiene, safe defecation, food safety, and the danger of open defecation fosters healthier practices and reinforces the benefits of WASH infrastructure [8,9]. School-based health education programs, in particular, have shown success in improving hygiene behaviours and reducing reinfection rates among children, the primary risk group for STH [2].

Despite decades of efforts targeting STH control, including school-based MDA programs and selective WASH interventions, reinfection rates remain high in many endemic countries, and evidence of long-term sustainability is limited. For example, in Kenya, five rounds of MDA resulted in significant reductions in prevalence, but persistent regional heterogeneity suggested retransmission due to environmental exposure and varying WASH conditions [10,11]. While cluster-randomized trials show that integrating school-based WASH interventions with deworming can reduce reinfection [8], these have not been accompanied by economic analyses assessing cost-effectiveness.

While significant economic evaluations have largely focused on drug delivery strategies, such as comparisons between community-wide and school-based MDA, these studies have reported mixed findings regarding effectiveness and equity [12]. There are far fewer studies that specifically assess the combined viability of WASH interventions across diverse transmission contexts.

While this scoping review does not test a formal statistical hypothesis due to its exploratory nature, it is grounded in a clear framework that outlines the expected links between the interventions and epidemiological outcomes. Standard preventive chemotherapy through MDA targets the individual parasite burden, leading to quick, temporary drops in prevalence and intensity. On the other hand, integrated WASH interventions aim to disrupt the environmental pathways through which STH eggs and larvae spread. Specifically, infrastructure elements such as safe water supply and improved sanitation facilities should reduce environmental faecal contamination. Meanwhile, behavioural aspects, such as promoting hand hygiene and providing health education, should reduce human contact with contaminated soil and water. Therefore, this integrated strategy is expected to show a combined effect, with the addition of WASH interventions to MDA resulting in lower reinfection rates and more sustained declines in STH prevalence than MDA alone can achieve.

With growing investment from both government and international agencies in WASH integration, it is imperative to map the existing literature on the impact and cost-effectiveness of WASH interventions on STH to inform resource allocation, identify evidence gaps, and guide the development of scalable models. Therefore, this study conducted a focused scoping review to provide critical insights for policymakers and donors seeking to optimize integrated WASH strategies in line with the WHO 2030 NTD targets.

2. Materials and methods

A review protocol for this study was published in the Open Science Framework on November 2, 2025, and can be accessed at (https://osf.io/kpmx3/files/uqb4e). The writing of the manuscript of this scoping review followed the Preferred Reporting Items for Systematic reviews and Meta-Analysis extension for Scoping Reviews (PRISMA-ScR) guidelines. The PRIMA-ScR checklist is available in the S1 Checklist. An initial search strategy and selection criteria were developed to guide this scoping review. This review was conducted to produce focused research in a timely manner. It followed the outline of Arksey and O’malley’s framework [13] by carefully focusing on the question, using broader search strategies, and extracting only key variables. The title, abstract, and full-text screening were conducted independently by two reviewers using predefined eligibility criteria guided by the Population-Concept-Context (PCC) framework. Discrepancies were resolved through discussion and consensus, with involvement of a third reviewer where necessary. Formal inter-rater statistics were not calculated, consistent with the exploratory nature of scoping reviews.

2.6 Study selection and screening

The selection of studies for inclusion in this scoping review followed a two-stage screening process: Title and abstract screening, followed by full-text screening. In the first stage, all records identified through the chosen database searches (i.e., PubMed and Google Scholar) were downloaded into a folder in Mendeley Reference Manager. We then screened the titles and abstracts of all retrieved citations against the eligibility criteria defined in the PCC framework. Studies were excluded at this stage if they were clearly irrelevant or did not focus on WASH interventions in relation to STH. In the second stage, we retrieved the full texts of all potentially eligible studies and reviewed them in detail against the pre-specified eligibility criteria (Fig 1).

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Fig 1. The selection process for studies included in the scoping review.

https://doi.org/10.1371/journal.pntd.0014664.g001

3. Results

4. Discussion

This scoping review synthesizes evidence on the impact and cost-effectiveness of water, sanitation, hygiene, and health education interventions integrated with MDA to control and eliminate STH. Overall, the findings demonstrate that integrated WASH approaches can improve STH control outcomes compared with MDA alone, particularly for A. lumbricoides. The review also reveals substantial gaps in economic evaluation, long-term effectiveness, and geographical coverage.

Recent primary research supports integrating WASH education into drug-based control strategies. A quasi-experimental study of Karen hill tribe communities in northern Thailand found that combining MDA with targeted WASH significantly reduced reinfection with intestinal parasites compared with MDA alone and was associated with significant improvements in participants’ knowledge, attitudes, and practices related to infection prevention [15]. Although the study did not evaluate comprehensive infrastructure improvements, the findings suggest that behaviour-focused WASH can enhance the short-term effectiveness of STH control efforts when paired with chemotherapy, particularly in resource-limited settings where poor hygiene practices and environmental exposure drive reinfection.

Observational evidence from the Geshiyaro project in Wolayita, Ethiopia, further underscores the importance of WASH access in controlling STH transmission. Using population-based cross-sectional data [24], it was demonstrated that both individual- and community-level access to improved water, sanitation, and hygiene were associated with a lower prevalence of A. lumbricoides, T. trichiura, and hookworm infections. Notably, community-level sanitation coverage showed stronger and more consistent associations with reduced infection than household-level access alone, suggesting that shared environmental exposure plays a critical role in sustaining transmission.

While randomized trials such as WASH for WORMS have significantly advanced understanding of the epidemiological impact of integrated WASH and deworming programs, they also highlight a persistent gap in economic evidence on cost-effectiveness. The WASH for WORMS cluster-randomized controlled trial in rural Timor-Leste found that a community-based WASH intervention integrated with periodic deworming did not yield additional reductions in STH infections beyond those achieved by deworming alone over a two-year period, despite substantial improvements in sanitation practices in the intervention arm [19].

In a community-based study in rural Bangladesh [23], a single round of albendazole was more cost-effective than regimens that included regular health education alongside chemotherapy for reducing the combined prevalence and intensity of A. lumbricoides, T. trichiura, and hookworm infections, suggesting that adding educational components did not improve cost-effectiveness in that setting. Although this study predates many contemporary WASH and integrated control strategies and did not evaluate comprehensive infrastructure improvements, it illustrates that health education alone may not offer cost advantages when combined with deworming and highlights the importance of rigorous economic analyses when considering additional WASH components.

Findings vary across studies, likely reflecting a combination of epidemiological and implementation-related factors. Differences in baseline transmission intensity, sanitation coverage, population density, and adherence to interventions may substantially affect the effectiveness of integrated WASH and MDA strategies. For example, in high-transmission settings with widespread environmental contamination, short-term WASH interventions may not be sufficient to produce measurable reductions in infection, even when improvements in hygiene behavior are observed [19,20]. In contrast, studies in settings with higher WASH intervention coverage have shown more pronounced reductions in infection [8,21]. These findings suggest that the success of WASH interventions is highly context-dependent and underscore the need for sustained, high-coverage implementation.

From a policy perspective, these findings reinforce the need to move beyond reliance on MDA alone and toward integrated, long-term strategies that address environmental transmission. While MDA provides rapid reductions in the infection burden, sustainable control will likely require investment in sanitation infrastructure, access to safe water, and sustained behavior-change interventions. However, the limited availability of cost-effectiveness evidence makes it difficult for policymakers to prioritize and scale these interventions, particularly in resource-constrained settings.

A key limitation of this scoping review is the lack of evidence on the costs and cost-effectiveness of integrating WASH interventions with deworming programs for STH control. Although numerous studies assess epidemiological outcomes, very few included economic analyses, and those that do are often outdated or limited in scope. This limits the ability to assess the value for money of integrated approaches and to compare them with standard MDA strategies, particularly in resource-constrained settings.

Another limitation concerns the screening process. Although study selection was conducted independently by two reviewers using predefined eligibility criteria, formal pilot testing and quantitative inter-rater reliability assessment were not conducted. Although discrepancies were resolved through discussion and consensus, the absence of pilot testing may have introduced minor inconsistencies in the interpretation of the eligibility criteria. However, the use of clearly defined PCC-based inclusion and exclusion criteria minimized this risk. In addition, the review focused primarily on key at-risk groups (children and women of reproductive age). While this aligns with standard WHO target frameworks, limiting the primary synthesis to these two cohorts may constrain the generalizability of our findings on community-wide transmission dynamics, where untreated or unmonitored segments of the broader population continue to contribute to environmental parasite contamination.

Finally, the review was limited by its reliance on two primary databases, PubMed and Google Scholar, for the peer-reviewed literature search. Although these databases provide extensive coverage of public health and economic research, some relevant studies indexed exclusively in other regional or specialized databases may have been missed. To mitigate this limitation, a comprehensive grey literature search was conducted across multiple institutional repositories, complemented by thorough backward citation tracking of all included articles.

5. Conclusion

Integrated WASH and MDA interventions show potential to enhance STH control and elimination, and reduce reinfection, particularly for A. lumbricoides. However, the strength of the evidence varies across settings and intervention types, and remains limited for certain parasites and outcomes. Further high-quality studies, including robust economic evaluations, are needed to better understand the effectiveness and cost-effectiveness of these approaches and to inform context-specific policy and implementation.

Supporting information

Acknowledgments

This study has been published with the permission of the Director General, Kenya Medical Research Institute.