Open Defecation and Downstream Water Quality in Nigeria: Fecal Contamination Pathways, Health Risks, and Modelling Approaches

Project Title: Open Defecation and Downstream Water Quality in Nigeria: Fecal Contamination Pathways, Health Risks, and Modelling Approaches - A Scoping Review Overview This project contains the registered protocol for a scoping review examining the relationship between open defecation (OD) and downstream water quality in Nigeria. The review is conducted in accordance with the methodological framework of Arksey and O'Malley (2005) as refined by Levac, Colquhoun, and O'Brien (2010), and reported following the PRISMA Extension for Scoping Reviews (PRISMA-ScR; Tricco et al., 2018). The protocol is registered here to ensure transparency, establish intellectual priority, and provide a public record of the methods used prior to or concurrent with the conduct of the review. Background and Problem Statement Open defecation remains one of the most critical public health and environmental challenges in Nigeria. Despite a global decline in open defecation rates, approximately 419 million people worldwide still practise it, with sub-Saharan Africa recording an increase rather than a decline (JMP, 2023). Nigeria accounts for the largest share of open defecation in sub-Saharan Africa, with approximately 48 million people still practising it as of March 2026, despite the Federal Government's Clean Nigeria Campaign launched in 2019 with a target of eliminating open defecation by 2030 (CNC, 2026). The public health consequences of open defecation are substantially mediated through the contamination of water bodies. Faeces deposited in the open environment are transported to surface water and groundwater through multiple pathways such as surface runoff from fecal fields during rainfall events, infiltration through the vadose zone to the water table, tidal and riverine transport, and direct discharge into water bodies. These pathways introduce fecal indicator organisms such as Escherichia coli, total coliforms, and Enterococcus, as well as waterborne pathogens including Vibrio cholerae, Salmonella typhi, Cryptosporidium, Giardia, and helminth eggs into water sources used by communities for drinking, domestic use, agriculture, and recreation. The resulting health burden is substantial. Diarrheal disease alone accounts for approximately 151,700 deaths annually in Nigeria, 16% of which are children under five years of age (UNICEF, 2021). Beyond mortality, persistent fecal contamination drives cholera outbreaks, typhoid fever, helminthiasis, stunting, malnutrition, and cognitive impairment, all of which hinder human capital development and economic productivity. Poor sanitation is estimated to cost Nigeria approximately 1.3% of GDP annually (Gayawan et al., 2023). Risk modelling tools, particularly Quantitative Microbial Risk Assessment (QMRA), provide a scientifically rigorous framework for estimating the probability of infection from waterborne pathogen exposure and for informing evidence-based water safety management. GIS-based spatial analysis, hydrological watershed models, and Bayesian spatio-temporal models offer complementary approaches for mapping contamination hotspots, simulating pathogen transport, and identifying temporal clustering trends. However, these modelling approaches have been applied in only a few isolated studies in Nigeria, with no integrated synthesis of their outcomes in relation to national sanitation trends. Justification for This Review There has not been scoping reviews to date that synthesised the evidence on open defecation-related fecal contamination pathways, associated waterborne health risks, and modelling approaches together specifically for Nigeria. Existing studies are fragmented across disciplines and geographic zones, frequently neglect socio-cultural variability, and rely on dose-response parameters developed for high-income settings that may not accurately reflect Nigerian exposure contexts. This limits the applicability of current evidence to national WASH policy, sanitation programming, and public health decision-making. A scoping review is the most appropriate study design for this purpose because the evidence base is heterogeneous in study design, outcome measures, and geographic scope, precluding statistical meta-analysis. A scoping review maps the extent, range, and nature of available evidence, identifies conceptual gaps, and provides a foundation for future primary research and systematic reviews on specific aspects of the topic. Objectives The primary objective of this scoping review is to map the extent, range, and nature of evidence on open defecation-related fecal contamination pathways, associated waterborne health risks, and modelling approaches applied to water quality assessment in Nigeria. The secondary objective is to identify evidence gaps and priority areas warranting future research to inform WASH policy and practice in Nigeria. The review addresses four specific research questions: 1. What fecal contamination pathways linking open defecation to downstream water quality degradation have been documented in Nigeria? 2. What waterborne health risks and disease outcomes associated with OD-related water contamination have been reported in Nigeria? 3. What modelling approaches, such as QMRA, GIS-based spatial models, hydrological models, and Bayesian models, have been applied to assess fecal contamination or health risk from open defecation in Nigeria? 4. What evidence gaps exist, and what future research priorities can be identified from the current body of literature? Methods Summary Eligibility is determined using the PCC framework. Population (communities in Nigeria exposed to open defecation and downstream water users), Concept (fecal contamination pathways, health risks, and modelling approaches), and Context (Nigeria, all six geopolitical zones, rural, peri-urban, and urban settings). All study designs are eligible. A differentiated date restriction is applied to primary research studies restricted to January 2015 to March 2026 to ensure empirical currency, while policy documents, grey literature, and foundational methodological papers have no date restriction. Searches were conducted across five sources in two phases. Phase 1 searches: PubMed, Google Scholar, and African Journals Online (AJOL) were conducted between February and March 2026 prior to protocol registration, yielding 1,490 gross records. Phase 2 searches: WHO IRIS and ResearchGate will be conducted following protocol registration. Hand-searching of reference lists and forward citation searching will supplement database searches. Screening will be conducted in Rayyan by two independent reviewers with Cohen's Kappa calculated for inter-rater reliability. Data will be extracted using a standardised charting form to capture bibliographic details, study design, water body type, contamination indicators, pathways documented, health outcomes, and modelling approaches. Results will be synthesised through narrative synthesis, descriptive quantification of study characteristics, and geographic mapping of included studies by Nigerian state. Expected Outcomes This review is expected to produce the following outcomes: A comprehensive evidence map of studies documenting fecal contamination pathways from open defecation to surface water and groundwater in Nigeria, including characterisation of seasonal and spatial patterns, proximity effects, and the relative contribution of different transport mechanisms across Nigeria's six geopolitical zones. A synthesis of health risk evidence quantifying the burden of waterborne disease attributable to OD-contaminated water in Nigeria, including diarrhoeal disease, cholera, typhoid, helminthiasis, stunting, and antimicrobial resistance, disaggregated where possible by age group, geographic zone, and water source type. A critical appraisal of modelling approaches applied in the Nigerian context, identifying which models have been used, their methodological strengths and limitations, the pathogens and water bodies modelled, and the risk estimates produced. This will identify whether existing models are adequate for informing water safety policy or whether new Nigeria-specific modelling frameworks are needed. An evidence gap map identifying understudied geographic zones, water body types, contamination pathways, health outcomes, and modelling approaches, providing a structured research agenda for future primary studies and systematic reviews. Policy-relevant conclusions for the Clean Nigeria Campaign, the SURWASH Programme, and Nigerian WASH policymakers, identifying where evidence is sufficient to guide intervention prioritisation and where critical knowledge gaps must be addressed before evidence-based policy can be developed. Intended Audience This review is intended for WASH researchers, environmental health scientists, public health practitioners, Nigerian government agencies including the Federal Ministry of Water Resources and state ministries of environment and health, international development partners including the World Bank and UNICEF, and journal reviewers and editors evaluating the submitted manuscript. Target Publication The completed review will be submitted for publication in the International Journal of Environmental Research and Public Health (IJERPH). Protocol Deviation Note Phase 1 database searches (PubMed, Google Scholar, and AJOL) were conducted prior to formal protocol registration on OSF due to unfamiliarity with pre-registration requirements at the project outset. Phase 2 searches (WHO IRIS and ResearchGate) are being conducted following registration. All methods described in the registered protocol accurately reflect the methods applied throughout the review. Full-text screening and data extraction had not commenced at the time of registration. This partial deviation is acknowledged as a limitation and is reported transparently in the published manuscript. Principal Investigator Saidat Oluwatoyin Shasore-Adetoro Federal Ministry of Water Resources, Abuja sshasore@gmail.com Co-Investigator Dr Adeleke Taofik Towolawi Fountain University, Osogbo Department of Environmental Health Sciences Files in This Project • Scoping_Review_Protocol.pdf - Full registered protocol including background, eligibility criteria, search strategy, data charting form, and deviation statement