Dissertation
Addressing the gaps in environmental safety: development of novel evidence and models to quantify enteric pathogen contamination in the environments of disparate geographic settings
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2023
DOI: 10.25820/etd.007119
Abstract
The purpose of this dissertation was to provide insight into two geographically disparate settings both experiencing microbial environmental contamination. Enteric pathogen exposure is a global problem that results in millions of cases of diarrhea each year and is the second-leading cause of death among children under five. The United Nations has placed universal access to clean water and safe sanitation, two of the primary risk factors, on its list of Sustainable Development Goals, which are its priorities to achieve by 2030.
This work first fills data gaps regarding private wells in an area that is vulnerable due to its karst geology and high prevalence of animal agriculture. Samples were collected from 102 private drinking water wells throughout Dubuque County, Iowa, USA and tested for enteric pathogens through selective agar culture plates, total coliform Colilert-18 tests, and quantitative Polymerase Chain Reaction (qPCR) assays. The samples with positive organism growth on plates were also analyzed for antimicrobial resistance using the Kirby Bauer disk diffusion assay. This yielded very high rates of growth on culture plates for Lactose-fermenting
Enterobacteriaceae, presumptive Shigella, presumptive Salmonella, and presumptive Campylobacter. The molecular methods demonstrated a high presence of Shigella and Shiga toxin producing E. coli. Of those organisms nearly all were resistant to erythromycin, a common antibiotic used in animal agriculture and human treatment. Colilert-18 tests did not have strong agreement with any of the qPCR or culture-based test methods for many of the specific organisms.
A multi-pathogen Bayesian exposure model was developed to understand how to interpret exposure risk from contamination data in the informal settlement of Corail, Haiti. The model incorporated environmental soil data from six enteric pathogen gene targets with observational behavioral data from hundreds of children playing in the public spaces of the community. The Bayesian approach allowed for interactions between the pathogens present for a more realistic model of the environment. The model’s posterior probability demonstrated that for some pathogens the risk of exposure was very low but for others it was as high as 0.22 during one hour of play in a public space. The model also demonstrated differences between developmental age categories with children and toddlers experiencing a higher likelihood of exposure and an increased exposure dose than infants.
In order to effectively combat environmental contamination and protect human health from exposure, environmental regulation needs to be strengthened with an increased emphasis on translating the available science into actionable policy. While there are many barriers to the science-policy pipeline, it is critical that our government prioritizes evidence-based policy and listening to scientific experts whenever possible. In conjunction, scientists need to become more active in communicating their science effectively and making sure it is presented in form usable by policymakers. My experience as a Knauss fellow in the U.S. House of Representatives provided me first-hand knowledge and understanding of the challenges to getting policy enacted, yet also inspired me to work to improve the science-policy interface in hopes of creating scientific consensus for better policy.
Preventing contaminants from reaching our environment and ensuring adequate remediation are necessary steps in decreasing public health risks due to enteric pathogens, but first it is critical to understand what contamination is in the environment and how it is reaching people. My research contributes to answering both of these questions in hopes of finding solutions to clean up the environment and protect people from enteric illness.
Details
- Title: Subtitle
- Addressing the gaps in environmental safety: development of novel evidence and models to quantify enteric pathogen contamination in the environments of disparate geographic settings
- Creators
- Stephanie A. Houser
- Contributors
- Kelly Baker (Advisor)David Cwiertny (Committee Member)Daniel Sewell (Committee Member)Craig Just (Committee Member)Nancy Hall (Committee Member)Ryan Jepson (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Civil and Environmental Engineering
- Date degree season
- Summer 2023
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.007119
- Number of pages
- xv, 149 pages
- Copyright
- Copyright 2023 Stephanie A. Houser
- Language
- English
- Date submitted
- 05/21/2023
- Description illustrations
- Illustrations, tables, graphs, charts
- Description bibliographic
- Includes bibliographical references.
- Public Abstract (ETD)
Bacteria and viruses from human and animal waste are often found in our environment and cause diarrheal disease, which is the second-leading cause of death among children under five worldwide. The first step in preventing disease is understanding where it comes from and how it is entering the human body.
One part of this dissertation focuses on understanding the bacterial contamination in groundwater in a vulnerable region of Northeast Iowa. We analyzed private drinking water wells in the region for several pathogens and found substantial indications of contamination and of antibiotic resistance, making resulting disease harder to treat.
This dissertation also used a statistical model to understand how many pathogens a child would be exposed to during one hour of play in a public space in a Haitian slum. We found that the likelihood was about 40% that a child would be exposed to at least one type of bacteria during an hour of play. The model also demonstrated that infants are less likely than toddlers and children to be exposed to bacteria during their hour of play in a public space.
Finally, this dissertation discusses the need for more scientific evidence to influence the creation and enactment of policies to protect our environment and promote human health. This section elaborates on my experience promoting science based environmental policy in the U.S. House of Representatives through a yearlong fellowship.
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9984454320002771
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