Grantee Research Project Results
2008 Progress Report: Examining Epidemiologic and Environmental Factors Associated with Microbial Risks from Drinking Water
EPA Grant Number: R831727Title: Examining Epidemiologic and Environmental Factors Associated with Microbial Risks from Drinking Water
Investigators: S. Eisenberg, Joseph N. , Moe, Christine L. , Uber, Jim
Institution: University of California - Berkeley , University of Cincinnati , Emory University
Current Institution: University of California - Berkeley , Emory University , University of Cincinnati
EPA Project Officer: Packard, Benjamin H
Project Period: December 23, 2004 through December 27, 2007 (Extended to December 27, 2009)
Project Period Covered by this Report: December 23, 2007 through December 27,2008
Project Amount: $589,806
RFA: Microbial Risk in Drinking Water (2003) RFA Text | Recipients Lists
Research Category: Nanotechnology , Drinking Water , Human Health , Water
Objective:
Results from drinking water intervention trials have provided a wide range of outcomes, ranging from no evidence of risk to attributable risk estimates as high as 35-40 percent. This range of risk estimates is problematic for regulators. One reason for this variation is because of the differing environmental conditions in each of these studies, such as source water concentrations, treatment barriers, and distribution systems. Risk models can provide insight to these epidemiologic data by interpreting the variability observed across studies. These insights then can be used to help design future studies. The objectives of this research project are to: (1) develop a population-based dynamic model that can be used to characterize drinking water risks to communities and apply this risk model to human calicivirus (HuCV), an important pathogen on the U.S. Environmental Protection Agency (EPA) Candidate Contaminant List; (2) develop an exposure model that describes the pathogen fate and transport from source water through to the distribution system for distribution systems representative of those in urban areas of the United States that will incorporate factors that have a potential role in determining human exposure; and (3) combine the models developed in Objectives 1 and 2 and conduct sensitivity studies to categorize those factors with respect to their relative importance in determining risk.
Progress Summary:
Interim Results
Progress in Year 4 of this project included: (1) the completion of our analysis of a NoV outbreak that provided a means to estimate household level transmission; (2) the development of a community based transmission model to analyze community based outbreaks; (3) the development of combined water sewage overflow (CSO) model; and (4) the start of three systematic reviews on infectious period of NoV infection, NoV occurrence data in wastewaters and surface waters, and NoV outbreaks.
Disease transmission model development for analysis of NoV outbreaks and the eventual use in MRA activities
Transmission is being modeled at two scales: household level and community level. One completed product is a statistical analysis of household-level transmission using a dynamic model, considering a specific scenario of a point source outbreak that spreads within households. The analysis focuses on a specific dataset that followed infected individuals within their households for a 10-day period. Current focus is on a community-level model that incorporates the household-level model as well as mixing between households, both directly and via shared public spaces (schools and work places). The study design focuses on outbreaks that may spread from one public location to another public location via household transmission, and thus requires the incorporation of social structure and the interaction of that social structure with the various factors that impact pathogen transmission (e.g., shedding duration, infectivity, asymptomatic shedding, and immune response). The product is a manuscript explaining the indirect risks associated with a point source outbreak.
Combined sewage overflow models to be used as a means to predict drinking water exposures
Here we have developed a simulation approach to explore and quantify these dynamics and their impact on environmental concentrations. We use a simplified model to predict statistical inputs of NoV into receiving waters, driven by precipitation events. In order to evaluate this model, we have developed a synthetic case study of NoV in a river basin, modeled after Ohio River and the known CSOs present between Louisville and upstream communities. Simulation to date focuses on only loadings due to NoV in raw sewage CSOs, ignoring loadings from treated water. These simulations could be extended to include discharge of NoV in treated sewage incorporating discharge volumes, treatment efficiencies, and seasonal variation in NoV concentration in raw sewage. In Year 5 we plan on conducting a basic risk assessment for NoV through source water exposure, based on the NoV dynamics driven by CSOs generated through simulation studies. We will use the NoV dose-response model presented in Teunis et al (2008), and water treatment effect estimates that are expressed as statistical distributions. Products include two manuscripts: (1) A description of our CSO model and how well it performs, and (2) synthetic simulation studies of NoV dynamics in a river basin, that is used as input for basic risk assessment.
Systematic Reviews used to help parameterize our health effects and exposure models
Shedding data: In order to support our population-level risk models, we need to better understand the duration in which people are infectious and are shedding pathogens into the environment. Our objectives here are to review studies that examine the lengths of time that people are shedding viruses focally, and compare the different datasets in light of the variability that exists in the study designs. The ultimate goal is to find a distribution that explains how long people will be shedding norovirus into the environment, integrating as much data as possible. Some of the factors that drive the distribution may include: demographic factors (age, general immune status), genotype differences, and detection methods. In addition, evidence of super-shedding (fecal shedding of norovirus for months to years as opposed to days) comes from data collected on immunocompromised individuals (cancer patients, transplant patients, people with genetic diseases). Products include a comprehensive review and statistical summary of shedding times, followed by simulations that look at the impact of variable shedding on disease transmission in communities.
Environmental occurrence data: The varieties of study factors present in the literature make it extremely difficult to quantify the real concentrations of infectious norovirus in the environment, and how the concentrations may change over time. There have been studies that examine and compare a limited set of these factors (e.g., norovirus in different media), but there seems to be little information that comprehensively looks at a wide variety of factors together, to fully integrate the maximum number of datasets. To support an exposure assessment model, we are characterizing the variability of the exposure data and trying to explain the observed variability through an analysis of a variety of study factors, including: seasonality, multiple environmental factors (e.g., temperature, microorganisms in water, water type – sea water versus fresh water, pH, turbidity), properties of the virus (strain), and sampling and detection techniques. In addition, we are examining non-environmental factors that will affect the observations, such as circulating infections within the population that can be measured through outbreak monitoring or other surveillance techniques. We have a particular interest in studies on seasonality. We have assessed datasets to see which can be used and compared. Objectives include determining which data are truly important to consider in terms of various environmental conditions, which genotypes to consider, and how to compare sampling and detection methods. Products include a comprehensive review manuscript, coupled with simulation studies that look at the importance of the temporal and other study factors to assess a population-level risk from norovirus through drinking water, including possibly a simple model that "closes the feedback loop” of disease dynamics affecting environmental concentrations, and vice-versa.
Future Activities:
During Year 5, we plan to complete our CSO exposure model, our transmission model ,and our systematic reviews.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 2 publications | 1 publications in selected types | All 1 journal articles |
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Type | Citation | ||
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Eisenberg JNS, Hubbard A, Wade TJ, Sylvester MD, LeChevallier MW, Levy DA, Colford Jr JM. Inferences drawn from a risk assessment compared directly with a randomized trial of a home drinking water intervention. Environmental Health Perspectives 2006;114(8):1199-1204. |
R831727 (2005) R831727 (2008) |
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Supplemental Keywords:
RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Water, Environmental Chemistry, Health Risk Assessment, Ecological Risk Assessment, Environmental Engineering, Drinking Water, microbial contamination, microbial risk assessment, monitoring, real time analysis, aquatic organisms, other - risk assessment, early warning, water quality, drinking water contaminants, epidemiological study, drinking water systemProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.