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3 Vulnerable Infrastructure and Waterborne Disease Risk OVERVIEW This chapter highlights an assortment of vulnerabilities in water and sanita- tion infrastructure and the various means used to assess their potential conse- quences on scales ranging from local to global. The first paper, by workshop speaker Michael Beach and coauthors from the Centers for Disease Control and Preventionâs (CDCâs) National Center for Zoonotic, Vector-Borne, and Enteric Diseases, demonstrates that the United States, despite its relatively light burden of waterborne disease, is home to a deteriorating public drinking water distribution system, increasing numbers of unregulated private water systems, and a limited, passive waterborne disease surveillance system. Beach and colleagues discuss major national trends in waterborne disease dynamics as detected by the CDCâs Waterborne Disease Outbreak Surveillance System (WBDOSS) and identify emerging needs in waterborne disease prevention and control, which include a deeper understanding of the ecology of waterborne disease as it pertains to drink- ing water distribution systems, safe water reuse programs, and an estimate of the burden of waterborne disease in toto to advocate for, as well as inform, active surveillance efforts. Climate change presents a serious challenge to safe water availability world- wide, for numerous reasons summarized by presenter Joan Rose of Michigan State University in the chapterâs second paper. In this context, she evaluates the findings of key studies relating health, climate, and water quality, and identifies critical questions for future research. Such studies have pursued three main lines of inquiry: 153
154 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH 1. Relationships between extreme weather events and outbreaks of water- borne disease; 2. Associated changes in fecal bacterial concentrations in water and climate factors; and 3. Quantitative assessments of the relationship between various environ- mental factors (e.g., infrastructure and climate) and transmission risk for specific waterborne pathogens. The essay concludes with a summary of critical needs that must be met in order to predict the effects of climate change on waterborne disease. The subsequent contribution, by speaker Kelly Reynolds of the University of Arizona and Kristina Mena of the University of Texas-Houston, expands on a topic introduced by Rose: quantitative microbial risk assessment of waterborne disease. Reynolds and Mena observe that human pathogens make difficult sub- jects for risk assessment due to their ârelatively low prevalence and infectious dose, specific virulence characteristics, and variably susceptible populationsâ; the vast diversity of water systems in use around the globe amplifies that challenge in the case of waterborne pathogens. Following a description of microbial risk assessment methodologies for waterborne disease, the authors review representative studies (most of which were conducted in the United States) that describe drinking water contamination and the role of the water distribution system in spreading waterborne disease, as well as that played by premise plumbing and the biofilms present therein. They discuss the potential for improving risk assessment science by taking full advan- tage of the complementary relationship between epidemiological and forecasting studies, and also with increasingly accurate mathematical models and improved monitoring capacity. That final, essential component of assessing risk for waterborne diseaseâ pathogen monitoringâwas the subject of a presentation in the same workshop session by Mark Sobsey of the University of North Carolina at Chapel Hill, entitled âCurrent Issues and Approaches to Microbial Testing of Water: Applica- bility and Use of Current Tests in the Developing World.â While clearly beneficial in industrialized countries, water testing is âessentialâ to providing safe water in developing countries, Sobsey observed. Water quality data informs the selection of promising sources for drinking water and appropriate treatments to ensure its safety, as well as the classification of existing sources for the purposes of studying their health effects. Unfortunately, he observed, most water tests are not acces- sible, are too complicated, or are too costly for use in developing countries. Sobsey described the ideal microbial water test for low-resource settings as portable, self-contained, lab-free, electricity-free, low cost, globally available, able to support data communication, and capable of educating and mobilizing stakeholders, especially youth, to improve public health. These goals eventually may be met through a variety of approaches and options but are currently lim-
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 155 ited mainly to culturing E. coli with enhanced detection. In the future, Sobsey predicted, culture-free and direct methods for detecting waterborne pathogens would predominate. These tests could be performed at ambient or body tempera- ture (on Petri films or absorbent pads, or in small volumes of liquid, that could be incubated in a pocket or armpit). They would display simple, picture-based, shareable results. Progress toward developing such a test is being made by the Aquatest ÂProject, an international, multidisciplinary consortium led by the University of Bristol, United Kingdom (Aquatest, 2009). âThe idea was to . . . develop a low-cost test that would be accessible and affordable for the developing world . . . sort of like a home pregnancy or glucose test,â Sobsey explained. Following a successful feasibility study, the project is now in its second phase: a four-year, $13 million- plus project funded by the Bill and Melinda Gates Foundation to develop a test for E. coli, field-test it in India and South Africa, and prepare to deploy it on a global basis. Sobsey concluded his presentation with the following recommendations to build on Aquatest and support continued development of microbial water tests for developing countries: â¢ Engage a wider network of collaborators and donors; â¢ Experiment with various test formats; â¢ Explore target microbes other than E. coli; â¢ Consider potential uses of testing results by a range of sectors (e.g., water science and engineering, health, and development); â¢ Link test development to waterborne disease epidemiology and quantita- tive risk assessment; and â¢ Use test as a tool for education and policy making.
156 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH The Changing Epidemiology of Waterborne Disease Outbreaks in the United States: Implications for System Infrastructure and Future Planning Michael J. Beach, Ph.D. Centers for Disease Control and Prevention Sharon Roy, M.D., M.P.H. Centers for Disease Control and Prevention Joan Brunkard, Ph.D.2 Centers for Disease Control and Prevention Jonathan Yoder, M.P.H., M.S.W.2 Centers for Disease Control and Prevention Michele C. Hlavsa, R.N., M.P.H.2 Centers for Disease Control and Prevention The timing for this presentation is fortuitous since it is September 23, 2008, the eve of the 100th anniversary of the addition of chlorine to the Jersey City, New Jersey drinking water supplyâthe first time chlorine was added to water to kill microbes and improve water quality at an American drinking water treatment plant. This centennial reminds us, as we explore current challenges in providing safe drinking water in this country, of the pivotal role that inclusion of filtration and disinfection in water treatment plants had in reducing the burden of water- borne diseases in the United States (Cutler and Miller, 2005). Since 1971, the Centers for Disease Control and Prevention (CDC) in col- laboration with the U.S. Environmental Protection Agency (EPA) and the Council for State and Territorial Epidemiologists (CSTE) has tracked epidemiological trends in waterborne disease in the United States through the national Waterborne Disease and Outbreak Surveillance System (WBDOSS). The WBDOSS receives investigative information on individual cases and outbreaks of waterborne disease from public health departments in states, territories, and the Freely Associated States (composed of the Republic of the Marshall Islands, the Federated States â Corresponding author. Associate Director for Healthy Water, National Center for Zoonotic, Vector- Borne and Enteric Diseases, Centers for Disease Control and Prevention, 4770 Buford Highway, F-22, Atlanta, Georgia 30341; E-mail: email@example.com; Tel: 770-488-7763; Fax: 770-488-7761. â Parasitic Diseases Branch, Division of Parasitic Diseases, National Center for Zoonotic, Vector- Borne and Enteric Diseases. â Information on the WBDOSS can be accessed at http://www.cdc.gov/healthywater/statistics/ wbdoss/index.html.
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 157 of Micronesia, and the Republic of Palau; formerly parts of the United States- administered Trust Territories of the Pacific Islands). Although initially designed to collect data about drinking water outbreaks in the United States, the WBDOSS now captures outbreaks associated with drinking water, recreational water, and nonrecreational water that is not intended for drinking or where the intended use is unknown. Annual or biennial surveillance summaries of the data have been published by CDC since the systemâs inception in 1971. This system is now the primary source of data on waterborne disease outbreaks (including those caused by pathogens, chemicals, and toxins) associated with ingestion, contact, or inhala- tion of drinking water, recreational water, or water not intended for drinking (i.e., cooling towers, industrial use) occurring within the United States. The WBDOSS has documented a wide range of outbreaks of waterborne illnesses including acute gastrointestinal illness (AGI), infections of the skin, ear, eye, respiratory tract, urinary tract, wounds, and neurological system. These include outbreaks of AGI caused by a variety of pathogens such as Campylobacter (Vogt et al., 1982), Cryptosporidium (CDC, 2007b, 2008b; Mac Kenzie et al., 1994; Wheeler et al., 2007), E. coli O157:H7 (McCarthy et al., 2001; Swerdlow et al., 1992), Ânorovirus (Parshionikar et al., 2003; Podewils et al., 2007), Giardia (Katz et al., 2006; Kent et al., 1988), Salmonella (Angulo et al., 1997), and Shigella (CDC, 2001; Iwamoto et al., 2005). Other nonenteric illness outbreaks have also been docu- mented in the United States and include illnesses such as Pseudomonas-related dermatitis/folliculitis and outer ear infections (CDC, 1982; Gustafson et al., 1983; Yoder et al., 2008a), adenovirus-related pharyngoconjunctival fever (DâAngelo et al., 1979; Turner et al., 1987), legionellosis (i.e., Legionnaireâs disease and Pontiac fever; Benin et al., 2002; Burnsed et al., 2007; Fields et al., 2001), echovirus-related aseptic meningitis (CDC, 2004), primary amebic meningoÂ encephalitis (CDC, 2008a; Visvesvara et al., 1990), hepatitis A (Bergeisen et al., 1985; Mahoney et al., 1992), leptospirosis (Morgan et al., 2002), and conditions caused or exacerbated by waterborne chemicals or toxins (for example, there are apparent links between bronchial health effects and chloramines, which are vola- tile irritants formed when nitrogenous waste such as urine or sweat is oxidized by hypochlorous acid used to disinfect swimming pools) (Bowen et al., 2007; CDC, 2007a, 2009; Kaydos-Daniels, 2008; Weisel et al., 2008). Trends in Drinking Water-Associated Disease Outbreaks Over the course of its existence, WBDOSS surveillance has revealed four major trends in drinking water-related outbreaks that reflect the positive impact â All WBDOSS surveillance summaries of data from 1971 to the latest summary can be found electronically on CDCâs Healthy Water website at http://www.cdc.gov/healthywater/statistics/wbdoss/ surveillance.html.
158 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH of regulation in improving drinking water safety in the United States, as well as where gaps in regulation exist: â¢ Public drinking water system-related disease outbreaks have decreased, reflecting the positive impact of national regulations (e.g., the Safe Drink- ing Water Act of 1974 and its amendments in 1986 and 1996; primary drinking water standards set in 1985; the Surface Water Treatment rule of 1989), as well as improved water system practices (Figure 3-1). How- ever, this apparent correlation of decreasing outbreaks with improved regulation underscores how disease prevention efforts must be maintained and improved. This includes a continued emphasis on enforcing and improving existing regulation as new data become available or new patho- gens emerge, implementation of new regulation as needed, source water protection, drinking water infrastructure investment, and other efforts responsible for the gains made to this point. â¢ The proportion of surface water-related disease outbreaks has declined in relation to groundwater-related disease outbreaks. Many regulations, including the Surface Water Treatment Rule of 1989, have focused on improving treatment of public drinking water supplies using surface water sources (e.g., rivers, lakes). It is therefore not surprising that while surface water-related disease outbreaks have decreased (Figure 3-2), Âgroundwater- â The Safe Drinking Water Act of 1974 put into motion a new national program to reclaim and ensure the purity of the water we consume. Under the Act, each level of government, every local water system, and the individual consumer have well-defined roles and responsibilities. But both the opportunity and the challenge of implementing the Act begins with EPA (for more information, see http://www.epa.gov/history/topics/sdwa/07.htm). â The 1986 amendment created a demonstration program to protect aquifers from pollutants, man- dated state-developed critical wellhead protection programs, required the development of drinking water standards for many contaminants now unregulated, and strengthened EPAâs enforcement powers in dealing with recalcitrant water systems and underground injection well operators. It also imposed a ban on lead-content plumbing materials. Studies have found that excessive levels of lead in drinking water can harm the central nervous system in humans, especially children. The measure also provides substantial new authority to EPA to enforce the law including increased civil and criminal penalties for violations (for more information, see http://www.epa.gov/history/topics/sdwa/04.htm). â The 1996 amendments established a strong new emphasis on preventing contamination problems through source water protection and enhanced water system management. This emphasis transformed the previous law, with its largely after-the-fact, regulatory focus, into a truly environmental statute that can better provide for the sustainable use of water by the nationâs public water systems and their customers. The states are central, creating and focusing prevention programs and helping water sys- tems improve operations and avoid contamination problems (for more information, see http://www. epa.gov/ogwdw/sdwa/theme.html). â The Surface Water Treatment Rule of 1989 was designed to prevent waterborne diseases caused by viruses, Legionella, and Giardia intestinalis. These disease-causing microbes are present at varying concentrations in most surface waters. The rule requires that water systems filter and disinfect water from surface water sources to reduce the occurrence of unsafe levels of these microbes (for more information, see http://epa.gov/ogwdw/therule.html#Surface).
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 159 50 45 40 Number of outbreaks 35 30 25 20 15 10 5 0 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 Year FIGURE 3-1â Number of reported waterborne-disease outbreaks in public drinking water systemsâUnited States, 1971-2006 (N = 680). SOURCE: CDC, unpublished WBDOSS data. 50% Figure 3-1 SWTR 1989 R01515 Percent of total deficiencies 40% vector, editable 30% 20% 10% 0% 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 Year FIGURE 3-2â Proportion of deficiencies in public drinking water systems associated with untreated or improperly treated surface waterâUnited States, 1971-2006. Defi- ciency = antecedent event or situation that results in exposure of persons to a disease- causing agent or agents. May be single or multiple deficiencies associated with each outbreak. SWTR = Surface Water Treatment Rule. SOURCE: CDC, unpublished WBDOSS data. Figure 3-2 R01515 vector, editable
160 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH 100% Percent of total deficiencies 80% 60% 40% 20% 0% 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 Year FIGURE 3-3â Proportion of deficiencies in public drinking water systems associated with untreated or improperly treated ground waterâUnited States, 1971-2006. Deficiency = antecedent event or situation that results in exposure of persons to a disease-causing agent or agents. May be single or multiple deficiencies associated with each outbreak. SOURCE: CDC, unpublished WBDOSS data. Figure 3-3 R01515 related disease outbreaks have continued to be reported (Figure 3-3). CDC is hopeful that the Groundwatereditable vector, Rule, published by EPA in the Federal Register in November 2006 (EPA, 2006), will eventually produce a decline in groundwater-related disease outbreaks similar to the results observed after enactment of the Surface Water Treatment Rule. â¢ Individual or unregulated water systems represent an important gap in waterborne disease prevention. Approximately 15.6 million householdsâ about 12 percent of U.S. householdsâreceive their water from private wells or small well water systems serving fewer than 25 people that are not regulated by EPA (U.S. Census Bureau, 2008). Although some of the smaller systems may be partially regulated by the state, private residential wells go unregulated. Generally, private well owners are not legally com- pelled to test or treat their drinking water, or to maintain the system to any standards. As a result, testing and maintenance schedules are likely to be less than optimal, resulting in increased vulnerability for well contamina- â The purpose of the rule is to reduce disease incidence associated with disease-causing microÂ organisms in drinking water. The rule established a risk-based approach to target groundwater systems that are vulnerable to fecal contamination.Â Groundwater systems that are identified as being at risk of fecal contamination must take corrective action to reduce potential illness from exposure to Âmicrobial pathogens.Â The rule applies to all systems that use groundwater as a source of drinking water (for more information, see http://www.epa.gov/safewater/disinfection/gwr/regulation.html and EPA, 2006).
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 161 tion. The potential ramifications for the health of children drinking private well water recently prompted an American Academy of Pediatrics policy statement providing recommendations for inspection, testing, and reme- diation for wells providing drinking water for children (AAP, 2009). As Figure 3-4 demonstrates, an increasing proportion of reported waterborne disease outbreaks are associated with use of individual private wells. â¢ Legionella is a continuing threat. Although the outbreak that led to the identification of Legionella as a pathogen occurred in 1976 (Fraser et al., 1977), only Pontiac fever, primarily associated with hot tub exposure, was reported to WBDOSS until 2001. In 2001, the system began captur- ing data on outbreaks of Legionnairesâ disease. In the latest surveillance summary (Yoder et al., 2008b), which covers drinking waterâÂassociated disease outbreaks reported from 2005 to 2006, half of all reported drinking waterârelated disease outbreaks were attributed to Legionella (Figure 3-5). Until Legionella outbreaks were included in the WBDOSS, AGI was the predominant type of illness associated with waterborne-disease outbreaks. Legionella, a thermophilic bacterium, colonizes and amplifies in premise plumbing systems (hot water heaters, taps, shower heads) as well as other sources of water (e.g., recreational hot tubs, cooling towers, etc.) and is transmitted by inhaling aerosols containing the bacterium (Fields et al., 2002). It can cause fatal pneumonia in vulnerable populations, such 100% Proportion of outbreaks 90% 80% 70% 60% Public (SDWA) 50% 40% Individual 30% 20% (Non-SDWA) 10% 0% 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 Year FIGURE 3-4â Percentage of waterborne-disease outbreaks in public and individual drink- ing water systemsâUnited States, 1971-2006 (N = 762). Excludes 18 outbreaks occurring in multiple system types at the same time, bottled water, bulk water purchase, and Âunknown system types. SDWA: drinking water systems covered by the Safe Drinking Water Act; Non-SDWA: drinking water systems not covered by the Safe Drinking Water Act. SOURCE: CDC, unpublished WBDOSS data. Figure 3-4 R01515 vector, editable
162 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH ARI (Legionella) 50.0% AGI 45.0% Hepatitis A 5.0% FIGURE 3-5â Percentage of waterborne-disease outbreaks associated with drinking water use, by illness and etiologyâUnited States, 2005-2006 (N = 20); ARI: acute respiratory illness; AGI: acute gastrointestinal illness. SOURCE: Yoder et al. (2008b). Figure 3-5 as residents of health-care facilities and nursing homes. Mycobacterium R01515 avium also appears to be vector, editable ecologic habitats colonized filling the same by Â Legionella, and it too has been associated with waterborne disease circle redrawn outbreaks (Falkinham, 2003). This underscores the need to focus on con- tamination of drinking water after it leaves regulated infrastructure, enters a building, or emerges at its point of use. Threats to drinking water safety from premise plumbing or public health challenges resulting from other uses of water (i.e., cooling towers, hot tubs) represent an important target for waterborne disease prevention. Limitations of Waterborne Disease Surveillance While the WBDOSS has been useful in elucidating the aforementioned trends and, therefore, highlighting areas of emerging public health need, this surveillance system has a number of critical limitations. First and foremost, the WBDOSS is a passive system based on outbreak reports from state and local public health agencies that do not necessarily actively track waterborne disease outbreaks. In many instances, waterborne disease outbreaks go unrecognized and therefore are neither investigated nor reported to CDC; thus, the WBDOSS provides, at best, an underestimate of waterborne disease outbreak occurrence
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 163 and trends. Waterborne disease outbreaks tend to be reported more consistently by health departments with adequate resources for investigation; therefore, the geographic distribution of reported outbreaks is unlikely to be representative of the true geographic distribution of outbreaks. Another shortcoming of WBDOSS is that it does not collect data on endemic waterborne disease. At this time, there are no reliable estimates of the total burden of disease for these illnesses in the United States. Several reviews of existing epidemiologic studies of drinking water use have produced preliminary estimates ranging from 4 million to 33 million cases of AGI per year that result from drink- ing water supplied by public water systems (Colford et al., 2006; Messner et al., 2006). However, these estimates need to be refined as better data and improved methods of estimating endemic waterborne disease become available. Further- more, these estimates do not include the full scope of waterborne illness in the United States (e.g., illness other than AGI), illness in the 15.6 million households served by private wells (U.S. Census Bureau, 2008), and illness in the more than 55 million swimmers using recreational water six or more times a year in the United States (U.S. Census Bureau, 2009). Emerging Challenges Drinking Water Distribution System Infrastructure Public drinking water systems in the United States supply 34 billion Âgallons per day of drinking water to approximately 87 percent of U.S. households (NRC, 2006; U.S. Census Bureau, 2008). The nationâs drinking water infrastructure contains more than 50,000 community water systems that rely on water treatment plants and distribution systems that include over one million miles of pipes plus associated pumps, valves, storage tanks, reservoirs, meters, and fittings (NRC, 2006). Most of the pipes in these systems will reach the end of their expected lifespan within the next 30 years; some are already overdue for replacement, as attested by water main breaks and the appearance of sinkholes in cities across the United States. Water pipes typically are located on top of sewers and sewer pipes. When water mains break, there is potential for contamination of the entire system. Based on a simple Google search for the term âboil water advisory,â hundreds to perhaps thousands of such incidents may occur in the United States each year. Such breaches in the water infrastructure result in costly repairs, increase the risk of water supply contamination, and impose a huge burden on local utilities and public health or environmental agencies. EPA has estimated that $276.8 billion will be needed over the next 20 years to repair and replace aging infrastructure, including $183.6 billion for transmission and distribution systems (EPA, 2005). Although the total number of drinking water-associated disease outbreaks has declined, the proportion of outbreaks caused by deficiencies in public water distri- bution systems (before the building point-of-entry) has been fairly consistent over
164 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH time, accounting for approximately 10 percent of drinking water outbreaks asso- ciated with public water systems since 1971 (CDC, unpublished data). However, this proportion would be expected to increase if infrastructure is not replaced on schedule. A recent epidemiologic study assessing the potential health risks associated with low pressure events in distribution systems found a relative risk of 1.58 (95 percent confidence interval: 1.1-2.3) for AGI following water main breaks or maintenance work in seven community water systems across Norway (NygÃ¥rd et al., 2007). According to the 2006 National Research Council (NRC) report, Drinking Water Distribution Systems: Assessing and Reducing Risks, the water distribution system is the one remaining component of U.S. public water systems yet to be adequately addressed to reduce waterborne disease outbreaks; thus, the committee recom- mended conducting epidemiological studies that specifically target the distribution system component of waterborne diseases (NRC, 2006). The Total Coliform Rule (TCR), which was intended to protect distribu- tion systems by testing for coliform bacteria, has been recently revised by EPA (2009a). Research and information collection priorities with respect to drinking water distribution systems in the revised Total Coliform Rule/Distribution System Advisory Committee (TCRDSAC) include the following (EPA, 2009b): â¢ Understand the role of cross-connections and backflow in system contamination. â¢ Learn how storage facility design, operation, and maintenance can influ- ence distribution systems and lead to contamination. â¢ Identify the best methods for installing and repairing water mains in order to reduce contamination. â¢ Assess the role of intrusions due to pressure conditions and physical gaps in causing contamination. â¢ Understand the significance of biofilm formation as an agent of water- borne disease, and identify effective controls for biofilm and microbial growth in water distribution systems. â¢ Study the role of nitrification in promoting bacterial blooms that contami- nate water systems. â¢ Determine safe methods for removing scale and sediment from drinking water distribution system components. Clearly the potential health impact of not replacing the nationâs drinking water infrastructure is high; investing funds over the next 20 years to upgrade and replace aging infrastructure is a public health imperative. Climate Change, Severe Weather Events, and Safe Water Availability The Arctic is the âcanary in a coal mineâ of climate change; the 4 million people in the Arctic are already experiencing the dramatic effects of rising tem-
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 165 peratures (Arctic Council and IASC, 2004). These include thawing permafrost and reduced pack ice that has led to massive coastal erosion, damaged water and wastewater infrastructure (some water systems have been washed away), breached waste lagoons, saltwater intrusion into water supplies, and increased organic loads in source water that challenge water treatment procedures. Habitat changes (e.g., increased ocean temperature, northern treeline movement) are projected to influence the distribution of zoonotic diseases that may impact water sources and human health (e.g., northerly beaver migration and giardiasis). Increasing ocean temperatures also seem tied to a recent Vibrio Â parahaemolyticus AGI outbreak associated with oyster consumption: this extended by 1,000 km the northern- most documented source of oysters contaminated with Vibrio Âparahaemolyticus (McLaughlin et al., 2005). Extreme weather events such as hurricanes, floods, and drought have debil- itated water treatment and distribution systems in many parts of the United States and elsewhere around the world, limiting residentsâ access to safe water. Extensive flooding in the midwestern United States in 1993 resulted in wide- spread and long-term contamination of wells in nine states (CDC, 1998). In 2008, severe drought limited water availability from Georgiaâs Lake Lanier, the main source of drinking water for the city of Atlanta. Severe weather (e.g., heavy precipitation, floods) appears to also be associated with increased report- ing of waterborne outbreaks (Curriero et al., 2001), and the potential impact of severe weather on waterborne disease is part of a larger discussion about potential climate change impacts on public health (Patz et al., 2000, 2008; Rose et al., 2001). One means by which the increasing impact of climate change and severe weather events on water availability can be addressed is by reusing wastewater. Indirect potable reuseâso-called âtoilet-to-tapââis not a popular option with the public. However, it is being utilized in places like Orange County, California, where up to 70 million gallons of highly treated wastewater per day are being injected into a groundwater aquifer to serve as a barrier to saltwater intrusion and to augment groundwater supplies needed for provision of municipal drink- ing water. In Gwinnett County, Georgia, a pipeline will soon deliver 60 million gallons of highly treated wastewater per day into drought-depleted Lake Lanier, Atlantaâs main water supply. The majority of water used in households does not flow through toilets but through showers, bathtubs, clothes washing machines, and sinks. If plumbing systems were designed to separate this âgraywaterâ from wastewater (i.e., toilets), graywater derived from these sources would be likely to have a low risk of patho- gen transmission and could be ârecycledâ for nonpotable household uses such as irrigation, exterior washing, and toilet flushing. Public awareness and education about water reuse is key to improving public perception and understanding about the range of water reuse options that will likely play a bigger role in supplying both potable and nonpotable water in the coming decades.
166 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH With increasing regional drought conditions, emerging conflict surrounding water rights and access, and competing demand for scarce water supplies, water reuse decisions are going to be a reality for more places in the future. To prepare for these decisions, we need new epidemiologic studies and methodological approaches to accurately measure the health effects of water reuse so that a sci- entific knowledge base is available for use by environmental, public health, and government officials. These decisions must balance the objectives of increasing water availability and protecting public health while being transparent to the general public. Recreational Water Use Perhaps lessons learned in preventing drinking waterâassociated disease can guide public health and the aquatics sector in combating dramatic changes in recreational waterâassociated disease in the United States. While the incidence of the drinking waterâassociated disease outbreaks has decreased over the last several decades (Yoder et al., 2008b), WBDOSS reporting has demonstrated a dramatic increase in the number of AGI outbreaks attributable to recreational water use in the United States (Figure 3-6). This increase is primarily due to an increased number of outbreaks associated with use of public swimming pools and other disinfected venues such as water parks and interactive fountains. The leading etiologic agent, Cryptosporidium, is extremely chlorine resistant, which allows the parasite to bypass the primary barrier to protecting swimmers from pathogens, 25 Treated 20 Untreated No. of outbreaks 15 10 5 0 8 80 82 84 86 88 90 92 94 96 98 00 02 04 06 7 19 19 19 19 19 19 19 19 19 19 19 20 20 20 20 Year FIGURE 3-6â Number of recreational water-associated outbreaks of acute gastrointestinal illness (n = 259), by water type and yearâUnited States, 1978-2006. SOURCE: Yoder et al. (2008a). Figure 3-6
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 167 chlorination (Korich et al., 1990; Shields et al., 2008). As a result, the parasite accounted for 68.3 percent of disinfected venue-associated outbreaks from 1997 to 2006 (Yoder et al., 2008a). In addition, enteric infections such as Salmonella and Shigella have also been linked to aquatic recreational activities despite traditional thinking about other exposures (e.g., food, child care centers; Denno et al., 2009). In natural, nondisinfected water (lakes, rivers, marine beaches), no barriers to transmission of pathogens are used. As a result, multiple studies from around the globe indicate that natural, nondisinfected water swimmers are at increased risk for AGI compared to nonswimmers (PrÃ¼ss, 1998; Wade et al., 2006, 2008). Other low incidence but severe outcome recreational water-associated infections such as those caused by Naegleria fowleri (primary amoebic meningoencephalitis; CDC, 2008a; Visvesvara et al., 1990) and Vibrio species (Yoder et al., 2008a) have also been reported to CDC. In the United States, waterborne disease associated with recreational water use likely results in a high level of morbidity. These challenges require a concerted effort to conduct sound research, develop and evaluate appro- priate interventions and strategies that address emerging issues such as chlorine- resistant microbes, and create a science-based regulatory framework that promotes healthy and safe recreational water use.10 Summary and the Path Forward Data suggest that the epidemiology of waterborne disease is changing in the United States. WBDOSS has documented decreasing surface water out- breaks, likely the result of drinking water regulation; increasing numbers of recreational water outbreaks, particularly associated with the chlorine-resistant parasite CryptoÂsporidium; the increasing importance of outbreaks associated with groundwater and private systems; the continued importance of Legionella as a pathogen and premise plumbing issues; and the ramifications of severe weather and potential climate change. New complexities have arisen that include an aging drinking water infrastructure, severe weather effects, water recycling, and recreational water use. To our detriment, those of us who study waterborne disease tend to compart- mentalize water. We attend drinking water meetings, recreational water meetings, water conservation meetings, and so on, but we too often fail to look at water- 10â All regulation of public pools in the United States is set at the state or local level. The lack of a uniform federal standard for public pool design, construction, operation, and maintenance has been recognized as a challenge for prevention of recreational water illnesses and injuries. Consequently, CDC is sponsoring a national effort, currently led by New York State, to develop the national Model Aquatic Health Code (MAHC). The objective of this knowledge-based and scientifically supported model health code is to reduce injuries and the transmission of pathogens at disinfected aquatic f Â acilities by making the best available standards and practices available for voluntary adoption by state and local health agencies. More information is available at http://www.cdc.gov/Âhealthyswimming/ MAHC/model_code.htm.
168 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH borne disease in toto. This challenge could be met by expanding discussions to include partners across the waterborne disease and water use spectrum. These discussions should involve all water uses (e.g., drinking, recreational, etc.), non- enteric as well as enteric disease, chemical challenges, water quantity as well as quality issues, and the implications of climate variability (e.g., drought, flood). This âOne Waterâ concept would strengthen our ability to address the full magni- tude and burden of waterborne disease and better reflect the full scope of effects of water on public health. In order to address the threat of waterborne disease over the long term, it will be essential to assess all types of water use, study the impact of both microbial and chemical contamination, and investigate the sources of human- and animal- specific contamination. This will require multiyear intervention studies, labora- tory methods development, and health-effects studies, involving state, local, and federal agencies, as well as academic researchers in the United States. FoodNet,11 an active surveillance system for foodborne illness in the United States, provides a model for such an effort, which could be used for designing a public health network for addressing key national questions related to waterborne disease. The development of âWaterNetâ with foundational and sustained funding could cre- ate or renew key strategic partnerships with multiple groups across a spectrum of disciplines, including epidemiology, clinical medicine, microbiology, laboratory, engineering, environmental and behavioral sciences, and health communications. Such a diversity of expertise will be necessary to identify and tackle key issues to reduce the burden of waterborne disease. The first step toward this goal should be to produce an accurate estimate of the overall waterborne disease burden, to be used as both a benchmark and an advocacy tool for resource allocation and priority setting. The specific objectives of âWaterNetâ should be the following: â¢ Determine the size of the problem. â Include all water types and uses (drinking, recreational, other) and both enteric and nonenteric illness. â Assess the prevalence of waterborne pathogens and chemicals in small water systems and premise plumbing. â¢ Increase investment. â Invest in building a science-based foundation of data for decision making. â¢ Enhance disease detection. â Improve detection, investigation, and reporting. â¢ Measure health effects of waterborne contaminants. â Invest in research on the health effects associated with drinking water infrastructure. â In particular, study chronic effects of chemical exposure. 11â See http://www.cdc.gov/FoodNet/.
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 169 â¢ Improve contaminant detection and removal. â Improve laboratory and epidemiologic capacity to sample, detect, and characterize waterborne contaminants in humans, animal reservoirs, and the environment. â Improve environmental tracking of contaminants. â Develop and evaluate methods for removing or inactivating contaminants. â¢ Promote access to water-related public health information. â Improve consumer knowledge and understanding of waterborne dis- ease and prevention. â¢ Develop prevention plans. â Test appropriate prevention interventions. â Develop and test adaptive strategies for water scarcity issues including conservation and reuse. â Develop sound, science-based public health policy to prevent water- borne disease. No natural resource is more fundamental to public health than water, and in the United Statesâwhere we are fortunate to have one of the safest water supplies in the worldâwe too often take it for granted. This paper has outlined some of the current water-related public health issues we face, but in the coming decades we will confront new and more intractable water and public health challenges. These include drought, decreased water availability and deteriorating water Â quality, aging water infrastructure, climate change impacts, chemical contamination, and the potential emergence of newly identified waterborne disease pathogens, which may be more difficult to combat because of chlorine or drug resistance. Preparing our public health system to address these challenges, as would occur if the proposed âWaterNetâ platform were implemented, would provide essential information needed to prevent waterborne disease and strengthen public health protection of U.S. water resources in the future. HEALTH, CLIMATE CHANGE, AND WATER QUALITY Joan B. Rose, Ph.D.12 Michigan State University Introduction The Intergovernmental Panel on Climate Change (IPCC) has predicted that global climate change will increase the threat to human health, ecosystems, and 12â Homer Nowlin Chair in Water Research, Michigan State University, 13 Natural Resources, E. Lansing, MI 48824. Phone: 517-432-4412; Fax: 517-432-1699; E-mail: firstname.lastname@example.org.
170 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH socioeconomic conditions (IPCC, 2007). Direct human health impacts are likely to be associated with increased extremes in the weather and climate patterns (e.g., temperature and precipitation) and disasters such as weather phenomena includ- ing floods, hurricanes, and tornados. But the role of climate change in the spread of infectious diseases is one area of human health which, due to the complex interactions between the environment (e.g., land and water) and people, and the high variability, is not well understood. Waterborne diseases, in particular, are influenced by distinct climate and weather factors that affect water pollution at water basin and watershed scales. In an attempt to improve our understanding and mitigate the potential for disease spread at a reasonably large geographic scale and at the community level, we will need to investigate further the relationships between health, climate, and water. Water resources and water-related disasters are key areas of concern in regard to climate and health. The recent IPCC report focused on the changes that might be expected, the causes, the projected effects, the need for adaptation and mitigation, and finally provided a long-term view of predictions. The relation- ship between climate and water resources has undergone extensive assessment (Roberson et al., 2008) and the key climate predictions that will likely affect water include: â¢ increased warming over land and at most high northern latitudes; â¢ contraction of snow cover; â¢ increased frequency of hot temperature extremes, heat waves, and heavy precipitation; â¢ precipitation increased at high latitudes and decreased at most subtropical land regions; â¢ increased annual river runoff and water availability at high latitudes and decreases in some dry regions in the midlatitudes and the tropics; and â¢ decreased water resources in many semi-arid areas (western United States). In addition, as a result of the increase in atmospheric concentrations of green- house gases, the frequency, intensity, and duration of extreme weather events is predicted to change. For example, more hot days, heat waves, and heavy pre- cipitation events are expected. The risks of floods and droughts in many regions would increase. Global annual precipitation is also projected to increase, although both increases and decreases in annual precipitation are projected at the regional scale. One of the necessary next steps beyond the assessment of extremes and water quantity changes is linking these changes to changes in water quality. Our ability to understand the effects of climate fluxes on the changes in water quality, which may in turn affect the likelihood of waterborne diseases, moves the field closer toward building predictive approaches that can be used for science and evidence-based management strategies. The research on water quality-health-climate interactions has focused on three main lines of evidence:
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 171 (1) human disease and climate, (2) changes in fecal indicators (pollution) in water associated with climate factors, and (3) changes in actual pathogen loading. And finally, research has begun to address adaptation and mitigation, primarily focused on water treatment. Human Disease and Climate: Waterborne Diseases Some of the strongest evidence now emerging is the association of precipita- tion as an extreme event with drinking waterborne disease outbreaks in the United States and Canada. About 50 percent of the outbreaks in the United States were statistically associated with extreme rainfall (at the 95 percentile compared to the 25-year average) and in Canada, rainfall events greater than the 93rd percentile were associated with outbreaks at a relative odds factor of 2.283 (95 percent [CI] = 1.216-4.285; Curriero et al., 2001; Thomas et al., 2006). Both surface water (Milwaukee, WI) and ground waters (Walkerton, Ontario; Put-In-Bay, Ohio) have been involved, and temporal differences have been suggested to be linked to the transport phenomenon (Auld et al., 2004; Curriero et al., 2001; Fong et al., 2007; Mac Kenzie et al., 1994). Globally, extreme rainfall remains the largest cause of both direct and indi- rect effects on human health and well-being. Flooding is the most frequent natural weather disaster (causing 30 to 46 percent of natural disasters in 2004-2005), affecting over 70 million people worldwide each year (Hoyois et al., 2007). The most common illnesses associated with floods described in the literature are d Â iarrhea, cholera, hepatitis (jaundice), leptospirosis, and typhoid. Unusual ill- nesses such as tetanus have also been reported. The etiological agents identified include Cryptosporidium spp., hepatitis A virus, hepatitis E virus, Leptospira spp., Salmonella typhi, and Vibrio cholera. Cholera in particular has been directly associated with flooding in Africa. In 1998, flooding in West Bengal was followed by a severe outbreak of cholera with 16,000 cases (Sur et al., 2000). Studies of flooding in Bangledesh in 1988, 1998, and 2004 confirmed that cholera was the most prevalent pathogen associated with floodingâincreasing by almost 20-fold (Schwartz et al., 2006). Also increasing were other fecal-oral pathogens including rotavirus Shigella, Salmonella, and Giardia (Schwartz et al., 2006). In Central America, Hurri- cane Mitch affected a large geographical area incluing Nicaragua, Guatemala, H Â onduras, El Salvador, and Belize. An estimated six feet of rain drowned crops, leading to food shortages. Gastrointestinal and respiratory diseases were rampant throughout the affected area. In Guatemala, the country most affected by cholera, the average weekly number of cases before Hurricane Mitch (January-October 1998) was 59, whereas after Hurricane Mitch (November 1998) the average number of cases per week was 485 (Figure 3-7; PAHO, 1998). There are many reports of devastating âoutbreaksâ associated with flooding. On May 5, 2005, outbreaks of waterborne diseases were reported as the death toll
172 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH 500 400 300 200 100 0 1 2 FIGURE 3-7â Cholera cases (1) pre and (2) post Hurricane Mitch in Guatemala in 1998. SOURCE: Based on data in PAHO (1998). rose into the hundreds in southeastern Ethiopia after flooding and heavy rains. In March 2006, a cycle of drought and Figure 3-7 flood in Malawiâs southern and central regions was reported to aggravate a cholera outbreak with many deaths reported. R01515 âMalawi is dealing with three crises atvector, editable the same time: food shortages, floods, and cholera,â said Dr. Eliab Some, who heads UNICEFâs health and nutrition team now b&w in Malawi (IRIN News, 2006). Over 4,000 cases of cholera, a disease associated with poor sanitation, lack of hygiene, and lack of access to potable water, have been recorded over the past three months, mostly in Malawiâs southern region. During the Tsunami of 2004, in the case of Aceh Province, many communi- ties reported diarrhea as the main cause of morbidity (85 percent of the cases were in children under five years of age), but neither increases in mortality nor out- breaks of cholera or other potentially epidemic diseases were reported Â(Brennen and Rimba, 2005). In some towns, more than two-thirds of the population died at the time of impact, almost 100 percent of homes were destroyed, and 100 per- cent lacked access to clean water and sanitation. To a large extent, the Australian army and other groups are to be credited with rapidly deploying environmental health teams to swiftly implement public health measures, including provision of safe drinking water, proper sanitary facilities, and mosquito control measures. Widespread fecal pollution of the surface waters was shown, yet the saltiness of the potable water supply after the disaster made much of the water unpalatable. Wells were vulnerable, perhaps to other etiological agents of fecal origin includ- ing viruses, and Shigella, with greater probability of infection than Vibrio, thus leading to the widespread diarrhea. After Hurricane Katrina, on the U.S. Gulf Coast, the lack of what was perceived or anticipated as an epidemic disease (thousands of cases) may have
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 173 been due to inadequate assessment and reporting (it was acknowledged that the public health response was grossly inadequate), dilution of sewage wastes, and rapid die-offs of pathogens of concern from the sewage-laden waters (due to the salinity and high temperatures). However, to imply that no infectious disease outbreaks occurred would be far from the truth. Vibrio vulnificus caused at least 22 wound-associated infections and killed five people (CDC, 2005a). In addition, a norovirus outbreak occurred among Katrina evacuees in Houston, Texas (CDC, 2005b). Disease reports of diarrheal illness steadily increased and jumped from 3 per 1,000 resident-days to 20 per 1,000 resident-days, within 5 days of exposure in the effected area (for evacuees in shelters). Reports of diarrheal illness peaked at 43.5 cases per 1,000 resident-days after an outbreak in a shelter was reported after day 7. Thus, there is much speculation about how much was or was not due to exposure to contaminated floodwaters (Cookson et al., 2008). Water Quality Changes in Fecal Pollution Indicators and Pathogens Associated with Climate In order to build an understanding of the public health risks associated with climate, the development of models of water quality changes are needed. However, initial studies have been without appropriate resolution in time, space, or hazard identification, and thus an adequate characterization of the quality, transport, fate, and variability of the microbial hazards is limited. There is no doubt that storm waters are laden with Escherichia coli and other fecal indicator bacteria; however, often the studies do not help to address risk of infectious disease transmission. Studies that provide good quantitative data at adequate spatial and temporal scales can begin to elucidate the interconnections between sources of the contaminants and risk of human exposure. Initial studies on El NiÃ±o in Florida demonstrated that over a 20-year time frame the impacts of such a climate signal on degrading water quality (based on fecal coliform indicator data) could be ascertained for the winter, spring, and fall months only (as the seasonal summer rains diminished any discernable change in either precipitation, river flows, and water quality; Lipp et al., 2001b). In addition, during the 1998 El NiÃ±o, increases in all fecal indicators, as well as virus pollution from presumably septic tanks, were related to the El NiÃ±o signal, which increased flow in two main rivers, impacting the Gulf of Mexico in Charlotte Harbor, Florida (Figure 3-8; Lipp et al., 2001a). Human viruses were only detected at the marine sites during this event. The other factor identified in this degradation of water quality associated with fecal pollution was water temperature. Thus, virus survival and dispersion were enhanced by low water temperatures and rainfall or river flow, respectively. Kistemann et al. (2002) have shown that not only do fecal indicators increase but the waterborne parasites Cryptosporidium and Giardia also increased signifi- cantly with rainfall and, thus, microbial loading associated with key rain events could be determined for the watershed. Interestingly enough, their assessment
174 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH Monthly ENSO SSTA Mean monthly discharge, Myakka and Peace Rivers Fecal coliform levels Enterococci levels Coliphage levels JFMAMJJASONDJFMAMJJASONDJF 1996 1997 1998 NiÃ±o Region 3.4 monthly sea surface temperature anomalies, mean monthly discharge from the Myakka and Peace Rivers, and water quality indicator levels (normalized to December, 1997) from Charlotte Harbor, Florida. FIGURE 3-8â Changes in water quality associated with septic tanks and the 1998 El NiÃ±o. SOURCE: Based on data in Lipp et al. (2001a). Figure 3-8 type replaced also demonstrated that the sources of the pathogens need to be present in the watershed for the predictions to hold true. While this seems obvious many scien- tific investigations fail to address the variability in pathogen types and concentra- tions in relationship to the sources, the climate event, and the disease outcomes. For example, studies after Hurricane Floyd showed significant water quality impacts via fecal indicators and in areas with high concentrations of pig farms that illnesses associated with specific etiological agents such as Â Adenovirus, Cryptosporidium, Giardia, Toxoplasma, and Helicobacter were not increased after the flooding even though unidentified illnesses did increase (from 5.1 to 11 outpatient visits per month). Key zoonotic pathogens that might have been pres- ent in the hogs, such as Salmonella and Campylobacter, were not investigated (Setzer et al., 2004). Although one might expect Cryptosporidium to be zoonotic, this disease is primarily associated with very young animals and more often with calves and lambs. While progress is being made on modeling of nitrates and other chemical constituents in floods and under key environmental conditions including land-use models, more studies are need on pollution-associated microbial infectious agents. The best work to date focuses on the naturally-occurring Vibrios associated with plankton in coastal waters (Lipp et al., 2002). These types of ecologically-based
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 175 models can also be useful for pathogens; however, much more data and informa- tion will be needed for the future. Quantitative Microbial Risk Assessment Approaches It is clear that the poor and developing countries will suffer the most severe consequences of climate and health changes. Here, I would suggest that sewage and human fecal pollution is the source; that climate is the driver of exposure; and, thus, one might hypothesize that the wastewater and drinking water infra- structure, the types of pathogens at any given time in the community wastewater, and the characteristics of the flooding would drive the risk of disease. In order to examine the parameters associated with the risk of disease transmission, a Quantitative Microbial Risk Assessment (QMRA) approach can be used for an extreme flooding event in a developing country where untreated sewage is mixed with water supply. This uses a standard procedure of hazard identification, expo- sure assessment, dose response relationship, and risk characterization (Haas et al., 1999). The pathogens Vibrio cholerae, Salmonella typhi, Cryptosporidium parvum, hepatitis A virus, and rotovirus were considered for the assessment (T. Shibata and J. B. Rose, QMRA for floods and disease, personal communication). Proba- bility of infection models were used (Haas et al., 1999) and assumptions based on published data on (1) occurrence in wastewater, (2) survival in the environment, (3) dilution during flooding, and (4) rates of ingestion were used to undertake a risk estimate. Crystal BallÂ®13 was used to develop a Monte Carlo simulation and to explore uncertainty analysis in health risk assessment. Figure 3-9 shows the preliminary outputs of the risk assessment. The high risk estimates for the viruses and parasites and the flat line over the first week demonstrate the impact of the high potency (infectivity) of these microbes and their enhanced survival compared with Vibrio, which has a greater potency than Salmonella. It should be noted that risks above 10â1 could be generally notable as outbreaks or increased rates of illness, while risks below that would likely only be observed with large epidemiological studies. This analysis suggests that higher risks could extend out 10 to 30 days for viruses and parasites compared to bacteria. Based on the literature, sewage concentrations for Vibrio are highly vari- able and were reported less so for hepatitis and Cryptosporidium. Thus, dilution played a larger role in defining the uncertainty of the risk for those pathogens. Over time, depending on the decay rates used, die-off in the environment played a significant role in defining the risk. Use of a QMRA begins to demonstrate the need for critical information to inform the relative level of risk. One can also begin to examine the relative 13â CrystalBallÂ® (Oracle Corporation, Redwood Shores, CA) is a statistical software package in which probabilistic simulations can be developed and run.
176 0 0 0 50% 50% 50% â1 90% â1 90% â1 90% â2 â2 â2 â3 â3 â3 â4 â4 â4 S. typhosa (Pi) V. cholerae (Pi) â5 â5 â5 Hepatitis A virus (Pi) â6 â6 â6 0 20 40 60 0 20 40 60 0 20 40 60 Time (days) Time (days) Time (days) 0 0 Sewage Dilution Decay Ingestion 50% 50% 100% â1 90% â1 90% 75% â2 â2 50% â3 â3 â4 â4 25% Contribution Ratavirus (Pi) â5 â5 0% Cryptosporidium (Pi) â6 Day Day Day Day Day Day â6 0 20 40 60 0 20 40 60 0 14 0 14 0 14 Time (days) Time (days) Cholerae Hepatitis Crypto FIGURE 3-9â Probability of infection from 10â1 to 10â6 for five pathogens over 60 days with 50th (yellow line) and 90th (blue line) percentiles of risk displayed. Bar graph demonstrates the uncertainty analysis associated with sewage concentrations of the pathogens (red bar), dilution (blue bar), decay or survival (green bar), and ingestion rates for cholera, hepatitis, and Cryptosporidium at Day 0 and Day 14. Figure 3-9 R01515 bitmapped image all type replaced
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 177 reduction in risk if interventions are used during flood events where sewage con- tamination is suspected. Critical Research Needs Schwartz et al. (2006) are to be commended for specifically defining the terms epidemic and flooding during their study; most do not. The term outbreak may or may not be used, regardless of the definition (greater than one case of disease from a common exposure, including venues [e.g., cruise ships, nursing homes, restaurants]; source [e.g., water, food, or an event]; picnic, flood). For example, the increase in Vibrio cases following Katrina certainly met this definition; how- ever, the CDC reported that no outbreaks had occurred. Floret et al. (2006) have titled their paper âNegligible Risk for Epidemics After Geophysical Disastersâ and they describe 26 large disasters, including 22 earthquakes, 2 volcanic eruptions, and 2 tsunamis. Of these 26 disasters, 19 percent reported either diseases such as giardiasis, pneumonia, Hep A and E respiratory, and/or diarrhea, and 8 percent reported no outbreak. The remaining 73 percent had no report. Of the more than 600 records, very few reported on infectious disease and of 233 articles retrieved from Medline, only 18 (7.7 percent) reported on infectious disease data collection. Epidemics and outbreaks were not defined and ânegligibleâ was not described based on values, economics, or any other measure. Many have suggested that this implies we have overexaggerated the risks and others have suggested that this means we have improved public health response during disasters, while others have argued that there has been inadequate surveillance and reporting. As seen in Figure 3-10, the risks associated with flooding or drought are far greater than other types of disasters. Therefore, it is clear that climate change must be considered; and given the nature of water, its importance and its widespread geographic impacts, the role of water quality and health must be addressed. Some of the critical needs that must be met in order to predict the effect of climate change on waterborne disease are â¢ better knowledge of disease incidence and pathogen excretion; â¢ better assessment of concentrations of pathogens in sewage and other sources; â¢ better assessment of the vulnerability of pathogen sources (e.g., combined sewer overflows versus septic tanks); â¢ better monitoring of sewage indicators to gather source, transport, and exposure information (event monitoring), and monitoring of sediments and other reservoirs; and â¢ more quantitative data for risk assessment. We will not be able to address the complexities of climate impacts on our water and our health without obtaining better health surveillance information and
178 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH Geological Windstorm 10% 26% Droughts & related Floods & related 19% 45% FIGURE 3-10â Percentage of disasters by type, 2000-2004 averages. SOURCE: Based on data in Hoyois et al. (2007). Figure 3-10 water quality data that are temporally R01515 and spatially relevant. Thus, as we move vector, editable forward in investing our own water infrastructure in the United States and develop redrawn serious programs to work at the global level, we should also invest in gathering the information and knowledge that will allow us to make informed decisions to assist in adaptation and mitigation strategies. Quantitative Microbial Risk Assessment of Waterborne Disease Kelly A. Reynolds, M.S.P.H., Ph.D.14 University of Arizona Kristina D. Mena, M.S.P.H., Ph.D.15 University of Texas-Houston The Risk Assessment Paradigm Risk analysis involves (1) the use of risk assessmentâcharacterizing a h Â azard qualitatively and quantitatively; (2) risk managementâincorporating the scientific assessment data with cultural values and ethics to determine appropriate 14â Environmental and Occupational Health, Mel and Enid Zuckerman College of Public Health, Tucson, AZ 85724. 15â Public Health, El Paso, TX 79902.
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 179 control actions; and (3) risk communicationâinvolving multiple stakeholders in an open discussion of the issues and opportunity to exchange information learned from the risk assessment and control options. Risk analysis is a controversial process where the social importance of specific impacts is not congruent across populations or among individuals. In contrast, risk assessment is a quantifiable concept. Using statistical concepts and mathematical modeling tools, estimates of risk can be related to a range of defined variables of exposure and dose response. Risk and uncertainty can therefore be quantitatively estimated, ultimately leading the risk characterization in populations and individuals. The basic risk assessment paradigm, published by the National Research Council (1983), provides a framework for the consistent application of risk analysis across multiple disciplines. These specific guidelines were intended to provide consistency to priority setting and the overall regulatory process of the federal government. Through the process of hazard identification, dose-response assessment, exposure assessment, and risk characterization, inferences become science-based and more credible with defined limits and measurable control benefits (Table 3-1). Although the steps in risk assessment are well defined, less certain is the accuracy of the assumptions we make in the process to estimate data where gaps exist. The need to standardize the risk assessment approach in making quantita- tive assumptions, while minimizing uncertainties, is apparent across multiple disciplines. TABLE 3-1â National Research Council Risk Assessment Paradigm Hazard identification Identification of hazards, incident scenarios, potential consequences, and agent properties, including factors of virulence, adaptation, resistance, and mutation. Includes consideration of acute and chronic health effects, sensitive populations, and individual immunity. Dose-response assessment Characterization of the relationship between dose and incidence of adverse effect in populations exposed to hazards. Exposure assessment Estimation of the frequency, amount, and duration of human exposures to agents via determined routes and the determination of the size and nature of the population exposed. Involves consideration of temporal and spatial exposure along with changes in microbial populations. Risk characterization Integration of information from hazard identification, dose-response assessment, and exposure assessment to estimate the magnitude (possibilities, probabilities, impacts) of health effects. Aided by tools in mathematical modeling and distribution analysis. SOURCE: NRC (1983).
180 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH Waterborne Disease Estimates Outbreaks of disease from drinking water are not common in the United States, but they do still occur and can lead to serious acute, chronic, or sometimes fatal health consequences, particularly in sensitive and immunocompromised populations. If properly applied, current protocols in municipal water treat- ment are effective at eliminating pathogens from water. However, inadequate, interrupted, or intermittent treatment has repeatedly been associated with water- borne disease outbreaks. Drinking water outbreaks exemplify known breaches in municipal water treatment and distribution processes and the failure of regulatory requirements to ensure that water is free of human pathogens. Numerous epidemiological studies have been conducted over the years to evaluate the role of drinking water in human illness; however, these studies are often criticized for their failure to consider all of the dynamic and complex interactions of the water treatment and distribution process relative to human exposures and eventual health endpoints. Risk assessment allows for the consid- eration of a wide range of exposure and impact scenarios but lacking is a defined and standard approach across the discipline. Proper study design is of the utmost importance for assuring the development of appropriate and effective policy and regulation. Drinking Water Contamination Waterborne disease outbreak data have been collected from the CDC, EPA, and CSTE since 1971. From 1971 to 2006, 841 documented outbreaks were associated with drinking water resulting in 578,829 cases of illness and 87 deaths (Blackburn et al., 2004; Calderon, 2004; Liang et al., 2006; Yoder et al., 2008); however, the true impact of disease is estimated to be much higher. Between 2005 and 2006, 28 outbreaks associated with drinking water were documented in the United States. These outbreaks, caused by human pathogens (including protozoa, viruses, or bacteria) and chemicals or toxins, resulted in 612 documented illnesses and 4 deaths (Yoder et al., 2008). According to a CDC survey, cross-connections and back-siphonage caused the majority (51 percent) of outbreaks linked to the distribution system from 1971 to 2000, followed by water main contamination (a collective 33 percent) and contami- nation of storage facilities (16 percent). Data compiled by EPA indicate that only a small percentage of contamination from cross-connections and back-siphonage are reported and that the CDC data underreport known instances of illnesses caused by backflow contamination events. For example, from 1981 to 1998, only 97 of 309 (31 percent) documented incidents were reported to public health authorities (AWWSC, 2002). Of the 97 reported incidences, 75 (77 percent) reported illnesses (4,416 estimated cases); however, only 26 (27 percent) appear in CDCâs summaries of waterborne disease outbreaks (reviewed in Reynolds et al., 2008).
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 181 National surveys and water utility databases are continuously growing. Recently, for example, several national surveys have documented evidence of viruses in groundwater (reviewed in Reynolds et al., 2008). The newly promul- gated Ground Water Rule requires that sanitary surveys are conducted by Decem- ber 31, 2012, for most community water systems (CWSs) and by 2014 for CWSs with outstanding performance and for all non-CWSs to help identify deficiencies that may lead to impaired water quality. Source water monitoring for indicator microbes, corrective actions for systems with significant deficiencies or source water fecal contamination, and compliance monitoring are further required. Using a risk-based approach, the EPA targeted groundwater sources at greatest risk of contamination rather than requiring all public water systems with a groundwater source to disinfect. The Ground Water Rule is estimated to reduce waterborne viral illnesses by approximately 42,000 cases each year (23 percent reduction from the current baseline estimate). Role of the Water Distribution System The distribution system is a complex network of pumps, pipes, and storage tanks that deliver finished water to end users (reviewed in Reynolds et al., 2008). There are approximately one million miles of distribution system networks in the United States and an estimated 154,000 finished water storage facilities with more than 13,000 miles of new pipes installed each year (AWWA, 2003; Grigg, 2005; Kirmeyer et al., 1994). Approximately 26 percent of the distribution pipes in the United States are in poor condition and the annual number of documented main breaks has significantly increased from about 250 in 1970 to 2,200 in 1989 (AWWSC, 2002). It is estimated that even well-run water distribution systems experience about 25 to 30 breaks per 100 miles of piping per year (Deb et al., 1995). Using a value of 27 main breaks per 100 miles per year, Kirmeyer et al. (1994) estimated 237,000 main breaks per year in the United States; however, variation between utilities is considerable. The public health significance of these breaks in the distribution system is not currently known. These data, and the sig- nificance of their inherent spatial and temporal variability, must be considered in future public health studies and risk assessment estimates. Calderon (2004) conducted a survey from 1991 to 2000 and found that the majority of outbreaks occurred due to a lack of treatment (primarily groundwater) or a treatment failure. During the 2003-2004 survey, approximately 52 percent of the contamination events occurred at the point of use (i.e., premise plumb- ing) while approximately 42 percent were due to source water contamination, treatment inadequacies, or contamination in the municipal distribution system. Little is known about the extensiveness of distribution system inadequacies and whether they are sporadic or continuously occurring (Lee and Schwab, 2005), but outbreaks have been documented following external contamination in the
182 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH distribution system despite the presence or requirement of residual disinfectant (Craun and Calderon, 2001; Levy et al., 1998). Other data that may be important to consider in distribution systems and contaminant exposures include hydraulic integrity, back-siphonage events, and intrusion rates. Water systems commonly lose more than 10 percent of the total water produced through leaks in the pipelines (AWWA and AWWARF, 1992). A survey of 26 water utilities in the United States found that the percent of leakage (unaccounted for water) ranged from less than 10 percent to as high as 32 percent (Kirmeyer et al., 2001). Compromised hydraulic integrity (positive pressure) of water distribution has been associated with worldwide epidemics (reviewed in Lee and Schwab, 2005). At least 20 percent of distribution mains are reported to be below the water table, but it is assumed that all systems have some pipe below the water table for some time throughout the year, thus providing an opportunity for intrusion of exterior water under low or negative pressure conditions (LeChevallier et al., 2003b). In addition, pipes buried in soil are subject to contamination with fecal indicators and pathogens from the surrounding environment (Karim et al., 2003; Kirmeyer et al., 2001). Even minor pressure fluctuations create back-siphonage, where intrusion rates are estimated at more than one gallon per minute (gpm; LeChevallier et al., 2003a). During power outages, up to 90 percent of nodes have been shown to draw a negative pressure (LeChevallier et al., 2003b). A survey of water utilities in North America found that 28.8 percent of cross-connections resulted in bacterial contamination (Lee et al., 2003). Negative hydraulic pressure can draw pathogens from the surrounding environment into the water supply, where residual disinfection efficacy is uncertain and variable, depending on the magnitude of such events (Gadgil, 1998; Haas and Trussel, 1998; Trussell, 1999). Little is known about the extensiveness of distribution system inadequacies and whether they are sporadic or continuously occurring (Lee and Schwab, 2005), but outbreaks have been documented following external contamination in the distribution system despite the presence or requirement of residual disinfectant (Craun and Calderon, 2001; Levy et al., 1998). Decline in residual disinfectant in the distribution system is related to many factors, including the distance traveled, water flow velocity, residence time, age and composition of pipes, and water pressure (Egorov et al., 2002). Although residual chlorine is present in the distribution system of treated water, the levels do not provide significant inactivation of pathogens in intrusion events (Payment, 1999; Snead et al., 1980). More recent modeling studies have evaluated intrusion events at specific locations, with consideration to mixing, contact time, and other distribution system variables, prior to consumption. Under these realistic expo- sure scenarios, monochloramine disinfectants performed poorly against Giardia and Escherichia coli. Typical concentrations of chlorine residual (0.5 mg/L) inactivated E. coli in simulated sewage intrusion events but were again Âineffective for Giardia (Baribeau et al., 2005; Propato and Uber, 2004). Intentional contami-
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 183 nation events in the distribution system are also a concern where public water supplies are potentially vulnerable to bioterrorism threats. Premise Plumbing/Biofilms Tap water is known to contain bacteria not found at the original source, treatment facility, or at other points earlier in the distribution system, indicating the possibility of biofilms in the distribution pipes or in the consumerâs tap (Chu et al., 2005; Pepper et al., 2004; Schmeisser et al., 2003). Bacterial colonization of pipes, connections, and faucets positioned along the channels of drinking water distribution, including the utilityâs distribution system, the homeownerâs distribution system (premise plumbing), and fixtures (i.e., faucets and hose con- nections) in the home, is well documented. Pepper et al. (2004) found that the bacteriological quality of water significantly deteriorates in home plumbing rela- tive to the distribution system, as evidenced by heterotrophic plate count (HPC) bacteria increasing up to five-fold from the distribution outlet to the household tap. Stagnant water in premise plumbing provides an environment where bacteria can grow to values several orders of magnitude higher than the municipal distri- bution system (Edwards et al., 2005). Legionella is a concern related to microbial growth in the distribution system. Ten waterborne outbreaks from Legionella occurred from 2005 to 2006 (Yoder et al., 2008). Legionella is known to grow in the distribution systems of large build- ings or institutions (Blackburn et al., 2004) and in premise plumbing (Thomas et al., 2006; Tobin-DâAngelo et al., 2004; Vacrewijck et al., 2005). These organisms remind us of the need to evaluate what specific effect(s) contribute to increased exposure to pathogens in the distribution system where not all systems present the same exposure scenarios and not all exposed populations will experience adverse impacts. H. pylori and Mycobacterium are also associated with biofilms, water distribution systems, and premise plumbing (Flannery et al., 2006; Park et al., 2001; Pryor et al., 2004). Epidemiological Research The true burden of waterborne disease is unknown in the United States, although variable approaches have been used to estimate gastrointestinal illness from waterborne pathogens, including epidemiological studies and exposure analysis. Information is lacking, however, regarding risk estimates that consider gastroenteritis and other illnesses. For example, household intervention trials have been used in an attempt to estimate the baseline of gastrointestinal illness within communities (Colford et al., 2002, 2005; Hellard et al., 2001; Payment et al., 1991, 1997). These epidemiological studies involved randomly designating one group of households as the âintervention group,â where members drank water additionally purified with an in-home treatment system, and then another group
184 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH drank tap water or water that passed through a sham device. In the latter situation, the study is blinded meaning that neither group knows during the study whether their in-home device is actually providing treatment. For all of these trials, the human health end point was gastrointestinal illness, with some variation in the specific definition of the symptomology. All participants were immunocompetent individuals who kept health diaries throughout the study to record symptoms related to gastrointestinal illnesses. The source (surface) waters were reported to have varying levels of micro- bial contamination. Other factors of inlet water quality and distribution system effects undoubtedly have some level of impact on end-use water quality and contaminant exposures. The initial study by Payment et al. (1991) concluded that an estimated 35 percent of the gastrointestinal illnesses occurring within the tap water group may be attributable to their drinking water. This was of interest given that the tap water met both Canadian and U.S. regulations. The source water, however, was subject to sewage contamination. One potential limitation in the study design was that persons drinking tap water were not provided a sham treatment device. In other words, the study was not blinded and thus participants may have been more inclined to report poor(er) health symptoms. A follow-up study attempted to evaluate the role of distribution system water quality in gastrointestinal incidence and involved four groups of participants: a tap water group and a bottled puri- fied water group (to address those exposed and unexposed, respectively), and a plant bottled water group and a tap water group using a purge valve (to address distribution system water quality). The attributable risk ranged from 3 percent for the bottled plant water group (rate of illness for this group is the same as for those drinking the bottled purified water), to 12 percent for the tap water group, to 17 percent for those in the tap water group with a purge valve. The investiga- tors concluded that the excess number of gastrointestinal illnesses observed was associated with contamination within the distribution system since the rate of illness of the bottled plant water group was similar to the rate of those drinking bottled purified water. This study was limited by population size since about half of the participants in the bottled plant water group dropped out during the course of the study. Another limitation was that this study, too, was not blinded. Addressing previous limitations, a blinded household intervention study was conducted in Australia (Hellard et al., 2001). Some participants used a water treatment device that involved an ultraviolet application and filtration while others were given a fake (no treatment) device. Unlike the Payment et al. (1991, 1997) studies, this study showed similar rates of illness of the participants in both the control and the intervention groups. Two more household intervention trials have since been conducted in the United States (Colford et al., 2002, 2005). After first determining that the study they designed could incorporate effective participant blinding, an attributable risk of 0.85 was observed, indicating that 24 percent of the gastrointestinal illnesses could be attributable to tap water.
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 185 In a follow-up study done by Colford et al. (2005), the investigators observed no difference in the rate of illness between the group with water treatment at the tap and those without. The authors offered the explanation that perhaps their study resulted in this conclusion due to successful water treatment practices and a well-maintained water distribution system. In addition, it was recognized that water consumption by the participants outside of the home may have had some effect on the study results. Similarly, community intervention studies have also been conducted to address waterborne gastrointestinal disease risks.16 Two of these studies ( Â Calderon, 2001; Goh et al., 2005) concluded that a reduction in gastroÂintestinal illnesses was observed due to the intervention (additional water treatment). A preliminary report from the Kunde et al. (unpublished) study also indicates a decrease in diarrheal illness risk in participants over age 35 following the intervention. Conversely, preliminary data analysis from the Frost study (unpub- lished) does not indicate a significant difference, however, analysis is reported to be ongoing for both of these aforementioned studies (reviewed in Calderon and Craun, 2006). The Role of Risk Assessment Conflicting results in replicate studies, as described earlier, indicate a flawed research design, inconsistent variables, or some other confounding effect. Con- tamination is not evenly distributed but rather is affected by differences in source water quality, hydraulic flow, mixing, biofilm development, age of distribution system, and many other variables that could explain inconsistent conclusions in epidemiological results. Even climatic events can play a role by taxing treatment plant operations or increasing the chances for environmental intrusion events. It is not practical to monitor water supplies in real time and at the point of use for all groups of contaminants; thus, episodic and routine contamination events are difficult to predict or identify. Epidemiological studies are often criticized for their lack of being properly controlled or randomized where the strength and validity of studies can be compromised by confounding factors, uncertainty, and inherent biases. Nonetheless, epidemiology is a vital component in determining risk factors for disease in a population. Well-conducted epidemiological studies contribute to improving the forecast of events as is done with quantitative risk assessment by providing more scientific rigor to the risk assessment process. Likewise, the process of quantitative risk assessment can be used to identify spe- cific effects of different types of data over defined, probabilistic ranges that have the greatest impact on health. This information can be used, in return, to better inform epidemiological studies. 16â See Calderon (2001), Frost et al. (unpublished), Goh et al. (2005), Hellard et al. (2002), Kunde et al. (unpublished), and McConnell et al. (2001).
186 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH Published guidance documents emphasize the need for improved data col- lection during drinking water outbreaks (Emde et al., 2001) and tools linking water utilities and health researchers (Parkin et al., 2006). Water utilities col- lect a plethora of water quality and distribution data, such as system types, sources, treatments, storage, quality indicator monitoring, residual disinfectants/Â alternative barriers, distribution flow/management, and consumer complaints. These complex databases have not been wholly integrated into risk assessment or health effects study design or analysis. Unknown are the implications these data have, both separately and in an integrated fashion, for the determination of human health risks from drinking water contaminants. Guidelines are needed to evaluate the robustness of available data relative to informing risk assessment and the study of population health risks. Recent estimates of waterborne illnesses per year in the United States range from 12 million cases/year (Colford et al., 2006) to 16 million cases/year ( Â Messner et al., 2006) to 19.5 million cases/year (Reynolds et al., 2008). Each estimate utilized a different approach and assumptions to calculate the public health risk. Using a proportional, risk-based approach, Colford et al. (2006) made assumptions under hypothetical scenarios of either poor source water quality/poor water treatment or contamination in a distribution system. The latter resulted in the estimated 11.69 million cases of acute gastrointestinal illnesses per year and a lower estimate of 4.26 million cases per year associated with poor source water quality/poor water treatment. Assumptions include the applicability of the attributable risk percent estimates from the household intervention trials to the entire U.S. population. The authors emphasize that the primary purpose of their estimation of acute gastrointestinal illness incidence, attributable to drinking tap water in the United States, is to demonstrate a methodology that can be improved upon with more data. This is an example of the necessary integration of risk assessment principles and epidemiological surveys to improve the rigor of each science separately. Quantitative Risk Assessment Quantitative risk assessment allows for the use of mathematical models to forecast public health impacts. By identifying a hazard and incorporating data such as the dose-response relationship and exposure information, we can esti- mate the health impact of those exposures. Messner et al. (2006) described a risk assessment approach for estimating the incidence of gastrointestinal disease in the United States due to drinking water (reviewed in Reynolds et al., 2008). Assuming that, for each population served by a community water system, a dis- tribution of incidence rates of acute gastroenteritis can be estimated. This rate can be applied to calculate a national estimate of disease attributable to drinking water in the United States. The authors speculate that the mean incidence of acute gastrointestinal illness attributable to drinking water among community water
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 187 systems ranges widely due to variations in source water quality, water treatment efficiencies, water quality within a distribution system, and water quality man- agement practices. Messner et al. (2006) proposed the development of a ârisk matrixâ to categorize community water systems based on relative microbial risk levels. The authors suggest connecting the information obtained from epidemiologi- cal Âstudies regarding the incidence rate of acute gastrointestinal illness to risk factors identified in the epidemiological studies that have been conducted and to other CWSs. The identification of these risk factors (characteristics) should allow for risk-based categorizing of other CWSs that have similar characteristics (therefore assuming that generalizations can be made regarding all U.S. CWSs and the populations they serve). Completing this process involves overcoming several challenges due to the lack of data related to both pathogen occurrence and variation in survivability and infectivity, as well as knowing the actual effi- ciency of water treatment applications (as opposed to theoretical information). Consideration of specific health-based information from previous studies with factors associated with source water/water treatment quality and distribution system deficiencies along with illness rates is warranted. Improved Monitoring Data Recent studies in water quality monitoring exemplify the multidisciplinary and innovative approaches needed to improve monitoring data that can be used to provide a more robust risk estimate. For example, characterization of com- plex transport phenomena provides necessary information related to assumptions of mixing within a pressurized water distribution network. Using a lab-scaled experimental setup of a distribution system and cross junctions equipped with various pumps and sensors, researchers are evaluating published models on water quality and hydraulic flow behavior of water distribution piping systems under various conditions of hydraulic flow. Studies conclude that previous assumptions of mixing in a distribution system are potentially in error. Minimizing these errors has practical implications for improving exposure estimates, determining water distribution infrastructure resilience, and evaluating impacts of a bioterrorism event (Austin et al., 2008; Kim et al., 2008; Romero-Gomez et al., 2008). Due to potential contamination in the distribution system and in premise plumbing, monitoring as close to the point of consumption as possible is war- ranted. Miles et al. (2009) described the use of a monitoring scheme at the neigh- borhood level for microbial pathogens and water quality indicators in municipal water supplies. Samples were collected from municipal water sources, subject to all federal water quality standards and regulations, post-treatment and distribu- tion. In this study, the current widespread network of water vending machines is utilized by collecting machine filters concentrating microbes from large volumes (thousands of liters) of source water over long time periods (several months). Of
188 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH the 45 filters from 41 unique sites, 10.4 percent and 6.3 percent tested positive for E. coli and infectious enteroviruses, respectively. Real-time monitoring remains an important goal in ensuring the consistent quality of the water supply. Rapid monitoring schemes are available for detection of viable bacteria and protozoa but not for human viruses. Viruses are known to cause approximately 8 percent of waterborne outbreaks in the United States. In addition, an etiological agent is not identified in about 40 percent of all water- borne outbreaks where the outbreak characteristics frequently indicate a viral agent (reviewed in Reynolds et al., 2008). Viruses present a particular challenge in monitoring water quality due to their small size, low infectious dose, and lack of universal cell culture. Conventional virus detection methods generally involve collection in the field followed by offsite analysis. Detection methods for viable viruses have high sensitivity and specificity but are costly, time-consuming, labor-intensive, and not applicable for the detection of some of the viruses of concern (i.e., noncytopathogenic viruses). Polymerase chain reaction (PCR) methods provide rapid detection but are complicated by inhibitory compounds in environmental samples and detection of nonviable agents. False positive and false negative results are common with each method (Reynolds et al., 1998). Integrating the two methods (integrated cell culture and PCR) has overcome major flaws of each individual method ( Â Blackmer et al., 2000; Reynolds et al., 1996, 2001). However, this approach is neither automated nor rapid. Advances in near-real-time monitoring for viruses in water include the use of electrodeposition of viruses onto the surface of optical fibers. Subsequently, infrared spectroscopy is used to characterize and identify captured viruses. Spe- cific and unique components of a virus present distinct vibrational fingerprints in the infrared (Wilhelm et al., 2008), which can be used to identify and quantify the type of virus. Regulatory Perspective Quantitative risk assessment is frequently used to formulate policy where acceptable risk limits are estimated from assumed exposure values gained from monitoring data. Current regulatory standards and monitoring requirements, however, do not guarantee the absence of human pathogens in tap water. For example, the Total Coliform Rule, mandating the use of bacterial indicators of water Âquality, does not predict vulnerability to an outbreak (Craun et al., 2002). In fact, few community and noncommunity water systems that reported an outbreak from the survey period of 1991 to 1998 had violated the coliform standard in the 12-month period prior to the outbreak. Risk limits are used to provide guidance on acceptable endpoints. The EPA suggests a risk of one case of disease in 10,000 persons exposed to potable water. This guidance is therefore used to conduct mathematical modeling of human
VULNERABLE INFRASTRUCTURE AND WATERBORNE DISEASE RISK 189 health risks from various agents to determine exposure standards or levels of contamination in various media that must not be exceeded. In addition, the neces- sary efficacy of preventative measures can be quantitatively evaluated to meet the acceptable risk level. For quantitative microbial risk assessment, key pieces of information are needed to be either known or predicted, including the infectious dose response of the pathogen of interest; concentration at which the agent can be found in water; the impact of various water treatment strategies on reducing pathogen infectivity; and pathogenicity factors. Values of exposure and dose- response parameters may correspond to a point estimate of interest. Typical point estimates may reflect the best calculation of risk or to a maxi- mum reasonable exposure or other justified value. Interval estimates are useful for looking at a range of values. In the latter, parameters are not single values but probability distributions. Risk assessment is subject to large uncertainty and vari- ability. Uncertainty occurs when there is an error in the estimate. For example, measurement errors, reporting errors, or inferences from a small, unrepresentative population lead to uncertainty in the estimate. Variability occurs due to intrinsic heterogenicity, such as differences in population consumption patterns, cultures and ethnicity, dose-response sensitivity, and immune function. The advantage of modeling probabilistically is to propagate these uncertainties through the model. Using distribution analysis, a range of possible outcomes can be assessed and key data contributors identified. A range of outcomes can be reviewed under dif- ferent conditions of uncertainty and mitigations to evaluate parameters that have the greatest health impacts. This process helps to define when better data can be most valuable and identify parameters that can be influenced by policy. Monte Carlo analysis is a widely applied tool for risk distribution analysis. Using random numbers in a computational process, a desired output as a func- tion of changing variables (i.e., dose, exposure, survival, etc.) can be estimated for known and assumed distribution inputs. The process can be easily repeated for thousands of trials. As part of the risk characterization process, however, a numberâor series of numbersâis needed to inform decisions about acceptable risk, possible risks, risk reduction potentials, and risk management decisions. Questions remain regarding acceptable risk limits, susceptible populations, and the use of conservative, worst-case, protective, or interval estimates. Recommendations and Conclusions While the discussion of how to appropriately estimate risks associated with contributing values continues, other factors must also be considered. We have learned that water quality variability affects long-term risk and that exposure is not constant over time. In addition, there is no threshold for infectivity with microbes. Even low-level exposures can have a significant impact on risk over time. Where average doses have been used in risk, the possibility of widespread exposure to low doses and limited exposures to large doses should be considered.
190 GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH Additional epidemiological data are necessary to prove the plausibility of models, and models should be evaluated with increased inputs related to the mechanisms of the host and pathogen interactions. In addition to the many variables in water quality, treatment, and distribu- tion, of particular concern are sensitive populations in the United States that are susceptible to higher rates of infections and to more serious health outcomes from waterborne pathogens. These subpopulations include not only individuals experiencing adverse health status, but also those experiencing ânormalâ life stages (e.g., pregnancy or those very young or old). Acceptable risk goals need to be evaluated for a changing population as persons move through these normal life stages that impact their susceptibility to waterborne illness. Risks may be acute or chronic and sequelae are common outcomes that must be considered (Parkin, 2000). With exposure-related inputs contributing the greatest uncertainty in models, more monitoring is needed to inform risk and minimize uncertainty in risk characterization. Finally, better communication between water quality professionals, public health researchers, and health-care providers is needed to design studies that comprehensively assess the impact of waterborne disease and address the multibarrier approach necessary to preserve water quality. OVERVIEW REFERENCES Aquatest. 2009. Aquatest research programme, http://www.bristol.ac.uk/aquatest/ (accessed April 15, 2009). BEACH ET AL. REFERENCES AAP (American Academy of Pediatrics). 2009. Drinking water from private wells and risks to chil- dren. Pediatrics 123(6):1599-1605. Angulo, F. J., S. Tippen, D. J. Sharp, B. J. Payne, C. Collier, J. E. Hill, T. J. Barrett, R. M. Clark, E. E. Geldreich, H. D. Donnell, and D. L. Swerdlow. 1997. A community waterborne outbreak of salmonellosis and the effectiveness of a boil water order. American Journal of Public Health 87(4):580-584. Arctic Council and IASC (International Arctic Science Committee). 2004. Impacts of a warming arctic. Cambridge, UK: Cambridge University Press. Benin, A. L., R. F. Benson, K. E. Arnold, A. E. Fiore, P. G. Cook, L. K. Williams, B. Fields, and R. E. Besser. 2002. An outbreak of travel-associated Legionnaires disease and Pontiac fever: the need for enhanced surveillance of travel-associated legionellosis in the United States. Journal of Infectious Diseases 185(2):237-243. Bergeisen, G. H., M. W. Hinds, and J. W. Skaggs. 1985. A waterborne outbreak of hepatitis A in Meade County, Kentucky. American Journal of Public Health 75(2):161-164. Bowen, A., J. Kile, C. Austin, C. Otto, B. Blount, N. Kazerouni, H.-N. Wong, H. Mainzer, J. Mott, M. J. Beach, and A. M. Fry. 2007. Outbreaks of short-incubation illness following exposure to indoor swimming pools. Environmental Health Perspectives 115(2):267-271. Burnsed, L. J., L. A. Hicks, L. M. Smithee, B. S. Fields, K. K. Bradley, N. Pascoe, S. M. Richards, S. Mallonee, L. Littrell, R. F. Benson, M. R. Moore, and Legionellosis Outbreak Investigation Team. 2007. A large, travel-associated outbreak of legionellosis among hotel guests: utility of the urine antigen assay in confirming Pontiac fever. Clinical Infectious Diseases 44(2):222-228.
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