Society For Risk Analysis Annual Meeting 2017

Session Schedule & Abstracts

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Common abbreviations

Symposium: Opportunistic Pathogens in Premise Plumbing

Room: Salon K   3:30 pm–5:10 pm

Chair(s): Kerry Hamilton

Sponsored by Dose Response and Microbial Risk Analysis Specialty Groups

Traditionally, water treatment efforts have focused on water leaving the treatment plant. However, today, a substantial portion of waterborne disease outbreaks in the United States can be traced to building plumbing systems. Recent outbreaks of Legionella in New York City and Flint, Michigan have raised questions about how to best manage risks in aging water systems. As public awareness of the need for water conservation, and new water-saving technology, have become increasingly effective at stemming excess water use, new questions are surfacing about how our plumbing, which was built to handle a regular flow of water, might now be a risk factor for bacterial and chemical contamination. Aggregate and per-capita usage has declined in many cities with decreasing populations and economic recession, resulting in higher water ages. Concurrently, plumbing codes have not adapted to these changes and oversized pipes exacerbate this issue. This session will give multiple perspectives on assessing the risks of opportunistic pathogens (Legionella, Nontuberculous mycobacteria, Pseudomonas aeruginosa, Naegleria fowleri, and Acanthamoeba spp.) in drinking water premise plumbing. An interdisciplinary perspective will be provided regarding use of appropriate dose response models, informing risk-based water quality targets, and quantitative frameworks for evaluating risk in the premise-plumbing context.

M4-I.1  3:30 pm  Opportunistic pathogen dose-response models. Mitchell JM, Dean KJ*, Tamrakar SB, Huang Y, Rose J; Michigan State University

Abstract: Opportunistic pathogens are ubiquitous in well-operated water distribution systems. Specifically, concerns about exposure to P. aeruginosa, L. pneumophila, M. avium, and N. fowleri through the water distribution and premise plumbing systems are of primary interests. These pathogens can grow in plumbing fixtures - shower heads and faucets - along pipe walls, and in water heaters. They are known to reside in biofilms and variations in usage or plumbing materials can lead to greater proliferation in the piping systems. In order to quantify the risk posed in these environments using Quantitative Microbial Risk Assessment (QMRA), a dose-response model for each pathogen is required to establish the risk of a health endpoint per given exposure dose. In terms of opportunistic pathogens in premise plumbing, the exposure dose could be reached by ingesting, inhaling, or being dermally exposed. Dose-response models for L. pneumophila and M. avium have previously been fit, but models need to be determined for other opportunistic pathogens. A literature review of dose-response studies for the opportunistic pathogens of interest was conducted and models were fit to selected data sets using the maximum likelihood estimation (MLE) with the “R” statistical programming package. Results showed that models for certain opportunistic pathogens were dependent on the route of exposure. For example, H. castellani having a beta-Poisson or exponential best fit depended on rather the data was fit to data from intranasal or intracardial exposures, respectively, as expected. For other pathogens, we assessed the variability in the degree of virulence across routes of exposure like for N. fowleri exposed via intranasal inoculation or through swimming. Because the overall risks for such pathogens is activity dependent it is important to evaluate these differences. This study produced new models for three pathogens emphasizing the importance of exposure route in the risk of an adverse response.

M4-I.2  3:50 pm  Non-consumptive Drinking Water Use and Microbial Risk – Do We Need a Safe Breathing Water Act? Bartrand TB*, Carotenuto AC; ESPRI Institute

Abstract: Safe Drinking Water Act (SDWA) regulations of drinking water microbial quality were developed primarily to manage risks associated with fecal pathogens and oral exposure. Because those regulations have been so effective, environmental pathogens and non-oral exposure routes (particularly inhalation) have emerged as critical drinking water hazards and exposures. This review identifies exposure pathways associated with non-consumptive uses of treated drinking water and pathogens relevant to those pathways. A wide list of relevant pathogens (bacteria, protozoa, amoebae, viruses, helminths, fungi) and their relevant exposure routes are presented and bellwether pathogens for use in developing risk managing strategies are identified. Assessing risks associated with non-consumptive uses is difficult for many of the reasons microbial risk assessment is difficult in general – sporadic occurrence of pathogens, poor association of relevant pathogens with indicator organisms or physicochemical indicators of water quality, and the long list of pathogens that could contribute risk. Pathogens relevant to non-consumptive use may originate in a building water supply and be transmitted through the building water system to a point of exposure, or grow in the building water system and be delivered during a non-consumptive use. In the first scenario, risk is assessed based on water quality of the building water supply and mitigated through treatment of the supply and monitoring. Assessing the risk in the second scenario requires knowledge of water quality of the building supply, the building plumbing system and the operation of the building water system. Mitigation can be via supplemental treatment, operational responses, or system redesign/retrofit. Competing risks arising from disinfection byproduct (DBP) exposure and scalding must be considered during development of risk mitigation strategies.

M4-I.3  4:10 pm  Reverse QMRA for opportunistic pathogens in premise plumbing. Hamilton KA*, Gurian PL; Drexel University

Abstract: The opportunistic premise plumbing pathogens (OPPPs) Legionella, Non-tuberculous Mycobacteria (NTM, including the Mycobacterium avium complex or MAC), Pseudomonas aeruginosa, Naegleria spp., and Acanthamoeba spp. are ubiquitous in water sources and occur widely in engineered water systems. Despite widespread exposure, human disease is relatively uncommon, except under circumstances where pathogen concentrations are high, host immunity is low, or exposures meet certain criteria such as inhalation of small-diameter aqueous aerosols. Still, OPPPs are key contributors to the United States waterborne disease burden and are responsible for a large portion of recent drinking-water related outbreaks. Water quality guidance values for Legionella and some other OPPPs are available for building water quality managers. However, these criteria are generally not risk-based. As a result, risk-based strategies for direct monitoring would be beneficial because pathogen monitoring can be costly. This study uses newly developed dose response models for OPPPs to conduct a “reverse” quantitative microbial risk assessment (QMRA) in which target risk values are used to back-calculate corresponding environmental exposures. These results can help to identify candidate ranges and influential data gaps that need to be addressed in order to develop meaningful water quality targets for use in larger-scale building water quality modeling efforts. This process is conducted for three different building types: conventional, water-efficient “green” buildings, and hospitals, in order to developed nuanced, location-dependent risk management guidance that takes into account differences in habitant exposure patterns and fixture types. A scenario analysis was conducted to investigate the impact of microbiological quality vs. an individual’s immune status or exposure pattern for the various fixture types. As a result, the feasibility of risk-based water quality targets is critically examined and alternative approaches are proposed.

M4-I.4  4:30 pm  Meta-Analysis of Legionella Interactions with Protozoa and Human Macrophage. Mraz AL*, Weir MH; The Ohio State Universtiy

Abstract: Legionella pneumophila (L. pneumophila) is the most common etiologic agent of Pontiac Fever and Legionnaires’ disease, respiratory diseases transmitted via waterborne aerosol inhalation. Legionellosis, a term incorporating both Legionnaires’ Disease, a severe pneumonia, and Pontiac Fever, a self-limiting flu-like illness, is the most common waterborne disease in the US, and its incidence is steadily increasing. L. pneumophila grows well in warm, stagnant, water (20-50°C), particularly in large distribution systems, such as those in hospitals or hotels. L. pneumophila thrives in biofilms, where it establishes and endosymbiotic relationship with protozoa, allowing the bacteria protection from disinfectants, such as residual chlorine. While there is a plethora of information regarding how L. pneumophila interacts with protozoa and human macrophages, this information has yet to be used for a comprehensive quantitative microbial risk assessment (QMRA) model for L. pneumophila in drinking water systems. This meta-analysis seeks to combine available data regarding the uptake of Legionella by protozoa and macrophages, the replication of Legionella in the host cell, the rates of exit from the host cell, and the rates of infectivity after leaving the initial host. We will be evaluating these rates in normal conditions, under particular genetic manipulations (e.g. dot/icm gene knockdowns), and under environmental stressors (e.g. chlorine treatment). In order to glean all applicable data available a critical literature review was performed. Data was selected from the literature based on if it would be appropriate to use in a mechanistic model (e.g. there are sufficient data points, the data is validated, the data informs Legionella’s ability to survive and thrive, etc.). The data will be used to build a QMRA model allowing scientists and engineers to further understand how environmental conditions effect Legionella’s virulence. This is an initial step in improved exposure control and therefore prevention of legionellosis outbreaks.


Abstract: Drinking water chemistry and microbiology inside buildings is a field of much needed scrutiny. Coupled with new innovative plumbing designs, low water use fixtures are increasing water age in buildings. Consequences of increased water age have shown to be related to off-tastes and -odors, reduced disinfectant residuals, production of disinfectant byproducts, and greater microbial levels, among others. A field study was conducted from September 2015 through December 2015 to understand the link between fixture water use and drinking water quality in a newly plumbed residential green building. Water use and quality were monitored at four in-building locations. Once the home was fully inhabited, the maximum water stagnation time found was 72 hr. Bacteria and organic carbon levels increased inside the plumbing system compared to the chlorinated municipal tap water entering the building. A positive correlation between organic carbon and bacterial concentration at select locations was observed. A greater number of bacteria was detected in hot water samples compared to cold water. This suggested that hot water plumbing promoted greater microbial growth. At some fixtures, metal plumbing components caused Zn, Cu and Pb levels to increase above the levels measured at the water treatment plant. At the basement fixture, where the least amount of water use events occurred, greater organic carbon, bacteria, and heavy metal concentration were detected. Different fixture use patterns resulted in disparate drinking water quality within the same residential building. Additional research will be described pertaining to organics release from plastic pipes, heavy metal fate in drinking water plumbing, along with other building plumbing research topics.

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