Health and Environmental Impacts of a Citywide Sanitation Intervention in Indiana

Safe sanitation is one of United States’ greatest public health achievements. Yet, regions remain where sanitation infrastructure is lacking that causes an attributable burden of disease. In the United States, this sanitation deficit includes combined sewer systems which are present in 700 municipalities and discharge 850 billion gallons of untreated wastewater to waterways annually. These overflows result in a wide range of exposures including during aquatic recreation, drinking water contamination, food contamination via agricultural irrigation, pathogen accumulation in fish and shellfish, and via mechanical vectors such as flies. Yet, the health impact of sanitation infrastructure upgrades aimed at reducing combined sewer overflows is largely uncharacterized. Enteric pathogens – which may cause diarrheal disease – and antimicrobial resistant organisms may be shed in human feces and are present in high concentrations in sewage. Recognizing the link between sanitation and public health, the city of Indianapolis is investing $3 billion in new sewerage that will nearly eliminate combined sewer overflows. The city experiences up to 90 sewer overflow events annually, which creates the unprecedented opportunity to study the environmental and health impacts of this intervention. Pre- intervention samples will be collected by the study team in 2025, construction will be completed in December 2025, and post-intervention samples will be collected in 2026. The proposed study will examine in detail the results of this sanitation intervention. Assessing the health impacts of city or neighborhood scale infrastructure is complicated by long construction timelines and it is difficult to randomize large infrastructure projects. This study aims to develop a novel framework using high level environmental outcomes to assess city scale sanitation interventions, which could be deployed globally. Surface water samples and flies will be collected and analyzed for fecal indicator bacteria, enteric pathogens, antimicrobial resistance genes, and fecal source tracking markers. The study will quantify the reductions of these targets in an intervention and control area. With this empirical data, quantitative microbial risk assessment (QMRA) will be used to determine the enteric infection risks attributable to aquatic recreation, use of contaminated surface water for agricultural irrigation, and contamination of food via flies. Novel risk assessment methods – that generate ratio measures of effect from QMRA outputs – will be used to evaluate the intervention. If successful, this study will advance our understanding of how to prevent the transmission of enteric diseases in communities reliant on combined sewer systems and combat the dissemination of antimicrobial resistant organisms.