Trends in diarrhoeal disease and improvements in household WASH indicators across Indian states: A comparative analysis of three National Family Health Survey rounds (NFHS-3 to NFHS-5)

Diarrhoeal diseases remain a significant public health concern in India, particularly among children under five years of age. Despite substantial improvements in access to safe drinking water, sanitation facilities, and hygiene practices over the past two decades, diarrhoeal morbidity continues to contribute to child illness and mortality in several regions of the country. Household water, sanitation and hygiene (WASH) conditions are widely recognized as key determinants of diarrhoeal disease transmission. In response to this challenge, India has implemented several large-scale initiatives such as the Swachh Bharat Mission and the National Rural Drinking Water Programme aimed at improving sanitation coverage and promoting hygienic behaviours. Evaluating whether these improvements in WASH infrastructure and practices have translated into measurable reductions in diarrhoeal disease is therefore critical for guiding public health policy and interventions. The proposed study aims to examine the temporal and regional trends in diarrhoeal disease prevalence alongside improvements in household WASH indicators across Indian states using data from three rounds of the National Family Health Survey (NFHS): NFHS-3 (2005–06), NFHS-4 (2015–16), and NFHS-5 (2019–21). These nationally representative surveys provide comprehensive information on household characteristics, child health outcomes, and environmental conditions across India. By analysing data from multiple survey rounds spanning nearly fifteen years, the study will provide insights into how diarrhoeal patterns have evolved over time and how these changes correspond with improvements in water, sanitation, and hygiene conditions. The primary purpose of the study is to identify and compare regional trends and patterns of diarrhoeal disease prevalence and household WASH indicators across Indian states over time. Specifically, the study will estimate the prevalence of diarrhoea among under-five children across the three NFHS rounds and assess changes in key WASH indicators such as access to improved drinking water sources, availability of improved sanitation facilities, presence of handwashing facilities with soap and water, and reduction in open defecation practices. In addition, the study will explore state-level and regional variations to identify geographical areas where diarrhoeal burden remains high despite improvements in WASH coverage. The study will employ a secondary data analysis design using publicly available NFHS datasets. Descriptive statistics will be used to estimate prevalence and distribution patterns, while comparative analyses will assess changes in diarrhoeal prevalence and WASH indicators across survey rounds. The analysis will also explore associations between WASH conditions and diarrhoeal prevalence to better understand the relationship between environmental health improvements and child health outcomes. Trends will be examined at both national and regional levels to highlight disparities across different parts of the country. The expected outcomes of this research include a comprehensive overview of the long-term trends in diarrhoeal disease and WASH conditions in India, identification of regions where improvements in WASH have been most pronounced, and recognition of areas where diarrhoeal disease remains disproportionately high. The findings will help determine whether improvements in sanitation and hygiene infrastructure have corresponded with reductions in diarrhoeal disease over time. Furthermore, the study is expected to highlight persistent regional inequalities and provide evidence that can support targeted public health strategies in high-burden areas. Overall, this research will contribute to the growing body of evidence on environmental determinants of child health in India and will provide valuable insights for policymakers, public health practitioners, and researchers working in the fields of epidemiology, environmental health, and health systems strengthening. By linking trends in WASH improvements with diarrhoeal disease patterns, the study aims to inform future interventions aimed at reducing the burden of preventable childhood illnesses and advancing progress toward national and global health goals.