Despite remarkable global progress, diarrheal disease remains the second leading cause of death among children under five, disproportionately affecting low- and middle-income countries (Troeger et al., 2018; Fagundes-Neto, 2013; GBD, 2016 Diarrhoeal Disease Collaborators, 2018; Wardlaw et al., 2010; Liu et al., 2016; Fischer Walker et al., 2012; Mills, 2014; GBD Diarrhoeal Diseases Collaborators, 2017). In Sub-Saharan Africa, over 13 % of total Disability-adjusted life years (DALYs) are attributed to diarrhea (GBD Diarrhoeal Diseases Collaborators, 2017; Tareke et al., 2022), with marked variation across the region (Liu et al., 2016; Reiner et al., 2018; Local Burden of Disease Diarrhoea Collaborators, 2020). These outcomes are shaped by limited access to water, sanitation and hygiene (WASH) services (Zerbo et al., 2021; Moise et al., 2024; Roche et al., 2017), low educational attainment (Moise, 2018), suboptimal management practices (Geldsetzer et al., 2014; Deichsel et al., 2023), and seasonal weather patterns such as rainfall and drought (Carlton et al., 2014; Wang et al., 2022). Sierra Leone exemplifies these challenges (Bah et al., 2022).

Facility-based data in Sierra Leone provide only a partial view of diarrheal disease burden. Many individuals do not seek care at health facilities and asymptomatic infections across age groups are rarely captured (Moise, 2018; Moise et al., 2016). Although a recent study noted strong child diarrhea management performance in Sierra Leone compared to twelve other Sub-Saharan African countries (Reiner and Hay, 2022; Carvajal-Vélez et al., 2016), case fatality rates still vary considerably (Reiner et al., 2018). To date, no research has documented the prevalence or incidence of diarrhea disease at the community level in the Rokel-Seli River watershed. This lack of localized data obscures the true burden in rural and peri-urban settings, where infrastructure and exposure vary widely.

Compounding this gap is a widespread lack of public awareness about diarrheal disease transmission and prevention. A recent study of 926 households (451 rural and 475 urban) across four districts in Sierra Leone found that residents had “limited knowledge about the transmission and prevention of diarrheal disease” (Sesay et al., 2023). These findings underscore the urgency of community-level surveillance and targeted health education, especially in regions where environmental and social determinants intersect. Despite definitional challenges, such as establishing culturally consistent criteria for identifying diarrheal episodes, fine-scale estimates remain essential for understanding community-level burden and guiding intervention strategies.

Sierra Leone has made notable investments in health system strengthening, including the Free Health Care Program and community case management initiatives (Diaz et al., 2013; Vallières et al., 2016; Maxmen, 2013; Moise and Ruiz, 2016; Dunn et al., 2012; Lo et al., 2017; Pielke et al., 2011; Taxiarchi et al., 2023). However, anticipated reductions in diarrheal disease have not been fully realized, particularly in under-resourced rural areas. Understanding the persistence of burden requires a more integrated and geographically sensitive approach.

This study responds to that need by leveraging a multi-scalar analytical framework that integrates spatial and non-spatial data. Rather than analyzing sanitation, land use and weather in isolation, we examine how these factors interact across geographic units (Deshpande et al., 2020; Mukabutera et al., 2016). This addresses a significant research gap, examined in greater detail in this study. By triangulating self-reported survey data with medical records, we estimate diarrheal disease prevalence and test hypotheses that would be obscured by single-source analysis (Deshpande et al., 2020). Importantly, we do not attempt to model climate change impacts, as our data are limited to one wet season and one dry season. Instead, we examine how local weather patterns specifically rainfall and temperature may influence diarrheal disease risk.

Our specific study aims include: (1) estimating community-level diarrheal disease prevalence in the Rokel-Seli River basin; 2) quantifying the role of social and environmental factors including water source, sanitation, education, population density on diarrhea disease risk, and (3) identifying salient geographic and biophysical predictors, including E. coli concentrations, land cover and topography. By situating this analysis within a specific ecological and social context, the study contributes to a growing body of place-based health research that emphasizes geographic specificity in understanding disease patterns and informing public health (Bah et al., 2022; Sesay et al., 2022, 2023; Lapworth et al., 2015; Papa et al., 2022; Singh et al., 2021; McMahon et al., 2013).