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Institute of Medicine (US) Forum on Microbial Threats. Global Issues in Water, Sanitation, and Health: Workshop Summary. Washington (DC): National Academies Press (US); 2009.

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Global Issues in Water, Sanitation, and Health: Workshop Summary.

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Workshop Overview

GLOBAL ISSUES IN WATER, SANITATION, AND HEALTH

Water is a fixed commodity. At any time in history, the planet contains about 332 million cubic miles of it. Most is salty. Only 2 percent is freshwater and two-thirds of that is unavailable for human use, locked in snow, ice, and permafrost. We are using the same water that the dinosaurs drank, and this same water has to make ice creams in Pasadena and the morning frost in Paris. It is limited, and it is being wasted. . . . But usage is only part of the problem. We are wasting our water mostly by putting waste into it.

Rose George (2008)

Worldwide, over one billion people lack access to an adequate water supply; more than twice as many lack basic sanitation (WHO/UNICEF, 2006). Unsafe water, inadequate sanitation, and insufficient hygiene account for an estimated 9.1 percent of the global burden of disease and 6.3 percent of all deaths, according to the World Health Organization (Prüss-Üstün et al., 2008). This burden is disproportionately borne by children in developing countries, with water-related factors causing more than 20 percent of deaths of people under age 14. Nearly half of all people in developing countries have infections or diseases associated with inadequate water supply and sanitation (Bartram et al., 2005).

The effects of water shortages and water pollution have been felt in both industrialized and developing countries, and it will be necessary to transcend international and political boundaries to meet the world’s water needs in a sustainable manner that will conserve and preserve this common resource. In the last few decades, national and international organizations from both the public and private sectors have come together to tackle global issues in water and sanitation.

The lack of access to and availability of clean water and sanitation has had devastating effects on many aspects of daily life. Areas without adequate supplies of freshwater and basic sanitation carry the highest burdens of disease which disproportionately impact children under five years of age. Lack of these basic necessities also influences the work burden, safety, education, and equity of women. While poverty has been a major barrier to gaining access to clean drinking water and sanitation in many parts of the developing world, access to and the availability of clean water is a prerequisite to the sustainable growth and development of communities around the world.

As the human population grows—tripling in the past century while, simultaneously, quadrupling its demand for water—Earth’s finite freshwater supplies are increasingly strained, and also increasingly contaminated by domestic, agricultural, and industrial wastes (UNESCO, 2006). Today, approximately one-third of the world’s population lives in areas with scarce water resources (UN, 2009). Nearly one billion people currently lack access to an adequate water supply, and more than twice as many lack access to basic sanitation services (Prüss-Üstün et al., 2008). It is projected that by 2025 water scarcity will affect nearly two-thirds of all people on the planet (Figure WO-1).

FIGURE WO-1. Population growth, climate change, reckless irrigation, and chronic waste are placing the world’s water supplies in danger.

FIGURE WO-1

Population growth, climate change, reckless irrigation, and chronic waste are placing the world’s water supplies in danger. SOURCE: Reprinted from Mittelstaedt (2009) with permission from The (more...)

The majority of these people live in rural areas without community infrastructure. With the rise of “megacities,” urban population growth may overtake the ability of local communities and governments to meet their residents’ water needs through infrastructure creation and improvements, adding to the estimated 3.6 million people who die each year from inadequate access to safe water, sanitation, and hygiene (Prüss-Üstün et al., 2008). Nearly one in four deaths among children under the age of 14 result from inadequate access to safe water, sanitation, and hygiene. Lack of these necessities also establishes a vicious cycle, for poverty bars many in the developing world from obtaining the safe drinking water and sanitation needed to drive sustainable community growth and development.

Recognizing that water availability, water quality, and sanitation are fundamental issues underlying infectious disease emergence, the Forum on Microbial Threats of the Institute of Medicine held a two-day public workshop in Washington, DC, on September 23 and 24, 2008. Through invited presentations and discussions, participants explored global and local connections between water, sanitation, and health; the spectrum of water-related disease transmission processes as they inform intervention design; lessons learned from water-related disease outbreaks; vulnerabilities in water and sanitation infrastructure in both industrialized and developing countries; and opportunities to improve water and sanitation infrastructure so as to reduce the risk of water-related infectious disease. 1

Some topics important to water quality and health were either not covered at the workshop, covered only in passing, or were explored in greater detail in other National Research Council (NRC) reports. These topics included desalination, 2 bioterrorism, 3 conflicts over water and the implications for global security, 4 pharmaceuticals, 5 heavy metals, 6 and issues related to runoff from farms and pollution of water supplies. 7

Organization of the Workshop Summary

This workshop summary was prepared for the Forum membership by the rapporteurs and includes a collection of individually authored papers and commentary. 8 Sections of the workshop summary not specifically attributed to an individual reflect the views of the rapporteurs and not those of the Forum on Microbial Threats, its sponsors, or the Institute of Medicine (IOM). The contents of the unattributed sections are based on the presentations and discussions at the workshop.

The workshop summary is organized into chapters as a topic-by-topic description of the presentations and discussions that took place at the workshop. Its purpose is to present lessons from relevant experience, to delineate a range of pivotal issues and their respective problems, and to offer potential responses as discussed and described by the workshop participants.

Although this workshop summary provides an account of the individual presentations, it also reflects an important feature of the Forum’s philosophy. The workshop promotes a dialogue among representatives from different sectors and allows them to present their beliefs about which areas may merit further attention. The reader should be aware, however, that the material presented herein expresses the views and opinions of the individuals participating in the workshop and not the deliberations and conclusions of a formally constituted IOM consensus study committee. These proceedings merely summarize the statements of participants at the workshop and are not intended to be an exhaustive exploration of the subject matter nor a representation of a consensus evaluation.

Global and Grassroots Perspectives

The workshop opened with a screening of the film Running Dry (Thebaut, 2005; CD included on the inside front cover of report volume), introduced and followed by remarks from its writer, producer, and director, James Thebaut. The documentary explores the growing global water crisis and its staggering toll of some 14,000 “quiet preventable deaths” per day. Focusing on China, the Middle East, Africa, India, and the United States, Running Dry presents compelling arguments for international cooperation on water issues and highlights some promising grassroots programs to improve access to safe water (see Chapter 1).

In China and India, rapid economic expansion has intensified demand for increasingly polluted water. China, the film notes, contains more than one-fifth of the world’s people but only seven percent of its fresh water (Thebaut, 2005). Industrial consumption of water drains the storied Yellow River to such an extent that in drought years, it runs dry. Seventy percent of China’s rapidly growing cities lack a sewage treatment plant, and agricultural and industrial waste pollutes the country’s major reservoirs. 9 Another fifth of the world’s population—and approximately half of the world’s poor—live in India, where more than 100 cities release their untreated human, animal, and industrial wastes directly into the sacred river Ganges, transforming it into an open sewer. This entirely preventable environmental catastrophe, coupled with widespread groundwater contamination, undoubtedly contributes to India’s heavy burden of death (Table WO-1) and disability (Table WO-2) from diarrheal disease.

TABLE WO-1. Estimation of Mortality Due to Diarrhea in India.

TABLE WO-1

Estimation of Mortality Due to Diarrhea in India.

TABLE WO-2. Data Used for Estimation of Burden Due to Diarrhea in India.

TABLE WO-2

Data Used for Estimation of Burden Due to Diarrhea in India.

Rampant over-consumption and misuse of water occurs in the United States, with consequences that reach well beyond our borders. Despite the existence of a bilateral treaty—the U.S.-Mexico Water Treaty of 1944 10 —that stipulates that the two countries will share the Colorado River’s waters, the demands of upstream users of the Colorado River—a primary source of water for seven states in the western United States—are now so great that its waters rarely reach the Sea of Cortez in Mexico (Cohen and Henges-Jeck, 2001). This is but one example among the growing number of social, political, and economic conflicts arising over access to water, according to Peter Gleick, cofounder and president of the Pacific Institute for Studies in Development, Environment, and Security (Gleick, 2001; Thebaut, 2005).

Where political tensions already exist—as in the arid Middle East—competition for and access to clean water, a natural resource more valuable than oil, 11 may intensify them. On the other hand, as both Shimon Peres, former Prime Minister of the State of Israel, and Nabil Sharif, Chairman of the Palestinian Water Authority, observed in Running Dry, the process of making policy to meet water needs may also offer adversaries an opening for resolving other conflicts. Extended to a global level, the necessity for international cooperation on water issues may thus be viewed as an opportunity for regional conflict resolution.

Water and Health in Africa

Africa poses particular challenges to providing safe, accessible water for its rapidly growing population. Although the continent, particularly in the Congo Basin, possesses abundant water resources, the majority of Africans lack access to safe water, primarily as a consequence of poverty and armed conflicts (UNICEF, 2006). Outbreaks of cholera and other water-related diseases have been frequent occurrences, affecting the health and well-being of thousands of individuals. In sub-Saharan Africa, water resources are scarce and water availability may be seasonal. According to the World Health Organization (WHO) and United Nations Children’s Fund (UNICEF) Joint Monitoring Programme for Water Supply and Sanitation (JMP), 28 percent of the population of sub-Saharan Africa defecates in the open, and an additional 23 percent use “unimproved” sanitation facilities that “do not ensure hygienic separation of human excreta from human contact” (JMP, 2008).

Moreover, even where clean water and flush toilets are available in Africa, lack of hygiene awareness continues to result in outbreaks of water-related diseases (Thebaut, 2005). Clearly, in order to benefit from advances in sanitation, people must appreciate the connection between water, sanitation, and health—a link that keynote speaker Donald Hopkins, Vice President of Health Programs at the Carter Center in Atlanta, Georgia, and his colleagues have tried to forge at the grassroots level in African communities (see Hopkins in Chapter 1). His description of two such programs with very different outcomes—one addressing trachoma in Ethiopia and the other targeting dracunculiasis (Guinea worm disease) in Ghana—revealed the importance of social factors as both catalysts and barriers to efforts to improve health in under-resourced communities by improving sanitation.

Trachoma in Ethiopia Trachoma, a chronic infection of the cornea 12 and conjunctiva 13 caused by the bacterium Chlamydia trachomatis, is the world’s leading preventable cause of blindness (Hopkins et al., 2008). Ten percent of the global population is considered to be at risk for developing this disease, which disproportionately affects females. Trachoma is transmitted through multiple routes, including contaminated fingers, flies, and fomites 14 such as dirty face cloths (Figure WO-2). The disease is currently managed through a multipronged strategy: surgery to prevent blindness in people with severe infections; antibiotics to fight infection in its early stages; educating people about the importance of proper face-washing to prevent the accumulation of discharge around the eyes; and environmental interventions such as improved sanitation to reduce populations of flies that spread the disease, and which breed mainly in human feces (Emerson et al., 2006; Hopkins, 2008; Hopkins et al., 2008).

FIGURE WO-2. The life cycle of trachoma.

FIGURE WO-2

The life cycle of trachoma. SOURCE: Reprinted from Dugger (2006). Copyright 2006 New York Times Graphics.

Of the approximately 50 countries where trachoma is endemic, Ethiopia is thought to have the largest number of cases; about one-third of these occur in the country’s impoverished Amhara region (Hopkins, 2008). Because this region’s geology and ecology favored the construction of latrines from abundant wood, Amhara provided a promising target for sanitation-based interventions to combat trachoma, Hopkins explained. Working with the Amhara Regional Health Bureau, and with local Lions Clubs, the Carter Center mobilized residents to build latrines. “There came to be a competition between villages, between families, in who could build the better latrine or the faster latrine,” he recalled, with much of the momentum provided by women. They welcomed the project because women without access to latrines were self-described “prisoners of the daylight” due to cultural taboos against women defecating in the open during daylight hours, when they might be seen by a man.

“This feminist aspect of this problem did not become apparent until we began this intervention . . . [and] it was not primarily to prevent trachoma,” Hopkins observed. Women’s demand for convenience provided “enormous energy” for the project, he said, and it was efficiently harnessed by organizing tightly knit kin groups to perform work that benefited their relatives, leaving little room for corruption. As a result, the program surpassed its initial goal to build 10,000 latrines in Ethiopia in 2004 by more than eightfold, and has continued to build a cumulative total of more than 600,000 latrines, as of mid-2008 (Figure WO-3). Even with subsequent declines due to political unrest and a focus on other diseases by the Carter Center, Ethiopia is well on its way to meeting the Millennium Development Goal (MDG; Box WO-1) for providing latrines to at least half of the population by 2015 that did not have latrines in 2000, he reported. Existing latrines in Ethiopia, and also those constructed in a similar project in Niger, are being used and in some cases upgraded, Hopkins reported. “The most important thing that has happened [as a result of this initiative] has been, not so much the physical act of building the latrine, but the change in the mindset,” he concluded. The behavioral foundations of this success should be studied so it can be replicated elsewhere, he added: “What we haven’t done, and can’t really afford to do, is to get some proper anthropologists and others to go into that area and really understand, better than we do, what happened there, to see how that can be applied more broadly, perhaps even beyond Ethiopia.”

FIGURE WO-3. Carter Center-supported household latrine construction in Ethiopia. *2008 data are provisional, January-August.

FIGURE WO-3

Carter Center-supported household latrine construction in Ethiopia. *2008 data are provisional, January-August. SOURCE: Courtesy of The Carter Center.

Box Icon

BOX WO-1

Millennium Development Goals. The Millennium Development Goals (MDGs) are based on the actions and targets contained in the Millennium Declaration, which was adopted by 189 nations and signed by (more...)

FIGURE WO-4. World population with and without access to an improved drinking water source in 1990, 2004, and 2015.

FIGURE WO-4

World population with and without access to an improved drinking water source in 1990, 2004, and 2015. SOURCE: Reprinted with permission from WHO/UNICEF (2006).

FIGURE WO-5. World population with and without access to improved sanitation in 1990, 2004, and 2015.

FIGURE WO-5

World population with and without access to improved sanitation in 1990, 2004, and 2015. SOURCE: Reprinted with permission from WHO/UNICEF (2006).

Dracunculiasis in Ghana Dracunculiasis 15 is caused by the nematode Dracunculus medinensis and is limited to humans, who typically ingest the parasite in water containing copepods 16 that carry the worm’s larvae (Hopkins et al., 2008). After a year-long asymptomatic incubation period, worms as long as one meter emerge through the skin on any part of the host’s body, causing extreme pain that, along with frequent secondary bacterial infection, typically incapacitates patients for two to three months (see Figure WO-6).

FIGURE WO-6. Guinea worm disease.

FIGURE WO-6

Guinea worm disease. SOURCE: Courtesy of The Carter Center/L. Gubb.

Half the population of a village may simultaneously experience these symptoms, drastically reducing school attendance and agricultural productivity. While there is no immunity to or cure for dracunculiasis, Hopkins noted, the disease could be eradicated by providing safe drinking water to vulnerable populations—a goal approached over the course of the past two decades, during which the number of infected individuals has declined from 3.5 million to 10,000 (Hopkins et al., 2008; Figures WO-7 and WO-8). Interventions included preventive health education and instruction in the use of cloth filters to remove copepods from drinking water; preventing contamination of surface water by infected persons discharging larvae from skin lesions; treating water reservoirswith a mild insecticide that kills copepods but does not harm humans, fish, or vegetation; and, most effective of all, providing clean water from underground borehole wells.

FIGURE WO-7. Number of reported cases of dracunculiasis by year, 1989–2007.

FIGURE WO-7

Number of reported cases of dracunculiasis by year, 1989–2007. SOURCE: Courtesy of The Carter Center.

FIGURE WO-8. Guinea worm reduction over time.

FIGURE WO-8

Guinea worm reduction over time. SOURCE: WHO Collaborating Center for Research, Training, and Eradication of Dracun-culiasis, CDC.

Despite the overall success of the dracunculiasis eradication campaign, some countries, including Ghana, continue to report thousands of cases per year, Hopkins reported. The highest rates of disease occur in the impoverished north of that country, where access to safe water is extremely limited due to scarce rainfall and geology that makes well-drilling difficult. As a result, residents are often forced to drink contaminated surface water. Hopkins observed, however, that the greatest obstacles to progress against dracunculiasis in northern Ghana were sociopolitical in nature. The country has been torn by often violent conflict among its several constituent ethnic groups. At the same time, official corruption at all levels of government and administrative “red tape” have rendered funded programs ineffective.

Because dracunculiasis is not fatal, and because its victims are mainly poor rural residents distant from the country’s southern power base, the political will to eradicate this disease is often lacking. Recalling his efforts to gain cooperation from the Ghanian government to address dracunculiasis in their country, Hopkins remarked that while he expected to encounter political fraud and corruption, he “was not prepared for the kind of indifference of people in agencies, in ministries, and the lack of a sense of urgency in getting help to these people, who were growing their food out in those rural areas.” Today, wells dug in northern Ghana through the efforts of the Carter Center and other nongovernmental organizations are largely useless, having fallen into disrepair or because they were inappropriately sited, he reported. Cloth filtration of water remains the best source of protection against dracunculiasis in northern Ghana. Since this method of water “purification” fails to remove bacterial or viral contaminants, it is far from optimal. He observed that “if it’s bad for children to have diarrhea, it’s worse for them to have diarrhea and Guinea worm disease.”

In reviewing the challenges and successes of the programs in Ethiopia and Ghana, Hopkins identified the following four lessons learned:

  • Priorities for clean water and sanitation—and thereby, health—must incorporate considerations of economics, politics, and geology.
  • Fraud, corruption, and indifference must be challenged in order to implement interventions to improve access to clean water.
  • Outcomes of water and sanitation interventions must be monitored to gauge and support their effectiveness over the long term.
  • It is better to implement limited interventions immediately than delay action until perfection is achievable.

Transmission and Prevention of Water-Related Diseases

The range of water-related microbial infectious diseases is vast, encompassing pathogens transmitted by diverse—and often nonexclusive—routes. While water quality affects transmission rates of many water-related diseases, water availability (or lack thereof) also plays a significant role in the spread of infection. Changes in water flow or quality, which can influence the population dynamics of vector species that transmit infectious diseases and intermediate hosts for microbial pathogens, also influence the prevalence and transmission dynamics of infectious diseases. Workshop presentations demonstrated how an analysis of transmission processes guides disease prevention efforts, and how such analyses may reveal the importance of the household as a target for clean water interventions.

Classification of Disease Transmission Processes

The first effort to classify the various routes by which water-related diseases may be transmitted, and thereby to relate transmission processes to potential interventions for disease reduction, was undertaken by workshop presenter David Bradley, of the London School of Hygiene and Tropical Medicine, and coworkers (White et al., 1972). In order to determine how best to reduce the burden of water-related disease using the limited resources available in East Africa in the 1960s, the researchers attempted “to disaggregate the various components of water-related disease and the way in which water affected them,” Bradley said (see Bradley in Chapter 1). They described four key categories of disease transmission processes: 17

  • Water-borne : The pathogen is acquired through consumption of contaminated water, as occurs in diarrheal diseases, dysenteries and typhoid fever.
  • Water-washed : The pathogen is spread from person to person due to lack of water for hygiene, as occurs in diarrheal diseases, scabies, and trachoma.
  • Water-based : The pathogen is transmitted to humans through contact with and infection, multiplication in, and excretion from aquatic intermediate hosts, as occurs in the diseases schistosomiasis and dracunculiasis (Guinea worm).
  • Water-related insect vectors : The pathogen is carried and transmitted by insects that breed in or bite near water, as occurs in dengue fever, malaria, and trypanosomiasis (sleeping sickness).

This classification scheme structures and clarifies information critical to effectively target interdisciplinary intervention efforts to the health effects of water and sanitation, which tend to be planned and executed by engineers, Bradley explained. Where once such efforts were limited almost exclusively to providing households with piped water, recognition of the importance of water-washed diseases led to an appreciation that, under some circumstances, simply making more water available—even without improving its quality—could provide significant health benefits. Bradley also adapted this classification scheme in order to estimate the relative burden of disease attributable to each type (Cairncross and Valdmanis, 2006); a modified version of the now well-known Bradley Classification of Water-Related Infections provides a framework for describing the spectrum of water-related diseases in Box WO-2.

Box Icon

BOX WO-2

Spectrum of Water-Related Diseases. Water-related infectious diseases are typically classified into the following four groups, based on their primary routes of transmission, in order to connect water (more...)

Bradley and coworkers have also identified six sanitation-related disease transmission categories, based on a combination of three key characteristics: latency of infectivity 18 following excretion, pathogen persistence 19 in the environment, and the ability of pathogens to multiply 20 in the environment (see Table WO-3). Various combinations of traits require different types of sanitary barriers in order to prevent disease transmission, as shown in Figure WO-8. Bradley said, for example, that while some transmission processes can be interrupted by providing latrines, this will not reduce transmission of “water-washed” pathogens that spread directly from person to person in the absence of adequate personal hygiene. In a given setting, preventive measures at the level of the individual (e.g., face washing), the household (e.g., latrine construction), or the community (e.g., sewage treatment) may be most effective, depending upon the sanitation-related transmission processes contributing to the local disease burden.

TABLE WO-3. Excreta-Related Transmission.

TABLE WO-3

Excreta-Related Transmission.

As Bradley discusses in his contribution to Chapter 1, the categories are related to the relative efficacy of various sanitary interventions. Human hygienic behavior (and particularly hand washing with soap) is most effective in the first two categories of disease transmission, the sanitary infrastructure affects categories II–IV the most, and the last two categories are most dependent on rather specific measures unless the general sanitary standard is relatively high.

These concepts, depicted in the cartoon for Figure WO-9, illustrate the anthropogenic components of human hygiene behaviors that are relevant to breaking the cycle of disease transmission and targeted prevention efforts.

FIGURE WO-9. Length and dispersion of transmission cycles of excreted infections.

FIGURE WO-9

Length and dispersion of transmission cycles of excreted infections. SOURCE: Reprinted from Feachem et al. (1983) with permission from the International Bank for Reconstruction and Development/The World (more...)

To further advance the understanding of disease processes provided by water- and sanitation-based transmission classifications, Bradley proposed the systematization of two additional transmission-related variables: hygiene behavior and spatial components of water and sanitation services. In the first case, echoing Hopkins’ earlier remarks, Bradley advocated an anthropological analysis of human behaviors relevant to disease transmission and prevention (Figure WO-9). In the second, he recommended the analysis of disease control on multiple spatial scales using geographical information systems, based on his observation that effective interventions to address water- and sanitation-related infectious diseases are often implemented at the local level but can achieve significant impact when replicated, with appropriate adaptations, in large numbers of other communities.

Disease Prevention at the Household Level

Despite significant progress over the past three decades in extending coverage in low-income countries, approximately one billion people lack access to improved water supplies, and many more rely on sources that are microbiologically contaminated (Clasen, 2008). While the provision of safe, piped water to every home is a distant goal, household-based water treatment and storage interventions represent important interim solutions for the prevention of water-related disease. Speaker Thomas Clasen, of the London School of Hygiene and Tropical Medicine, noted that a systematic review and meta-analysis of 57 studies comparing the bacterial content of drinking water at its source with water stored in the home (Wright et al., 2004) found that in many settings, the bacteriological quality of drinking water declined significantly after collection. The authors concluded, therefore, that policies that aim to improve water quality at the source may be compromised unless they are accompanied by corresponding measures to ensure safe household water storage and treatment.

The profound disease burden attributed to diarrhea makes it the most important target for waterborne disease prevention, Clasen said. Following respiratory infections diarrheal diseases are the second leading cause of deaths from infectious disease, and the second leading cause of childhood mortality, exceeded only by neonatal conditions (Black et al., 2003). Following a systematic review of intervention trials to improve water quality, Clasen and his coauthors concluded that household-based interventions were nearly twice as effective as source-based measures for preventing diarrheal disease (Clasen et al., 2007b). 21 Similarly, workshop speaker Pete Kolsky, of the World Bank, and coauthors concluded that “the householder’s perspective and priorities are similar to those that emerge from a public health perspective. As most of the victims of poor environmental health are children under five, it makes sense to focus attention on where they spend the most time, which is at home” (Bostoen et al., 2007).

Workshop presentations by Clasen and Robert Tauxe, of the Division of Foodborne, Bacterial and Mycotic Diseases at the U.S. Centers for Disease Control and Prevention (CDC), described a range of household-based (also known as point-of-use) strategies to improve water quality and thereby reduce the burden of water-related disease. Clasen (see Chapter 4) noted that the most common method of household water treatment is boiling. Although highly effective in reducing microbiological contamination, boiled water can be readily recontaminated. Furthermore, the physical process of boiling water is relatively costly in terms of time and energy, is associated with a small but measurable risk for burn accidents, and contributes to indoor air pollution as well as carbon emissions depending on the carbon source(s) used as fuel to boil water (Clasen, 2008; Clasen et al., 2008). Despite these shortcomings, the widespread use of boiling indicates good potential for the adoption of household water treatment methods that are more effective, more convenient, less costly, more appealing, less hazardous, and more sustainable.

Tauxe described strategies to improve the quality of the water obtained by individual households for drinking, washing, and food preparation, and to maintain its purity during storage in the home (see Tauxe et al. in Chapter 1). He and coworkers have studied the specific health effects of a variety of interventions to make unsafe water safer to drink, as well as ways to increase the uptake of these interventions through social marketing. Their combined water chlorination and storage “safe water system,” sold for a low price in Africa under the brand name WaterGuard®, 22 has proven to be scalable, sustainable, and measurable in its health benefits, Tauxe reported. In a study conducted in households in Uganda containing at least one member with HIV, use of the safe water system for one year was associated with a 20 percent reduction in diarrheal episodes among all family members, and a 25 percent reduction among those with HIV (Lule et al., 2005). This finding, coupled with the results of 20 additional published studies on point-of-use water chlorination, provides strong evidence that this intervention reduces the risk of childhood diarrhea, among other health benefits (Arnold and Colford, 2007).

Tauxe observed that in addition to providing measurable protection against diarrheal diseases, safe water programs can serve as a springboard for additional public health interventions to tackle water-related infectious diseases. Combined initiatives promoting hand washing and the use of the safe water system, conducted in maternal and child health clinics and in schools in both Kenya (O’Reilly et al., 2008; Parker et al., 2006) and China (Bowen et al., 2007), have led to measurable improvements in hygiene behavior, as well as in health measures such as reduced school absenteeism. Moreover, researchers found that children in school-based hand hygiene and safe water programs positively influenced their parents’ behavior. “The parents reported that they picked up more WaterGuard® [and used it] . . . more often,” Tauxe said. “There was more soap in the home, and there was a lot of hand washing going on.” Based on these successes, similar interventions are currently being expanded to serve 1,500 Kenyan schools and are being assessed in schools in Pakistan and the Philippines.

The availability of safe water also supports a safe food supply. At the local level, Tauxe reported, safe water systems have been shown to reduce contaminants such as E. coli in food prepared in the home and by street vendors. However, as global markets expand, the quality of water used to grow, harvest, and process produce and other foodstuffs for worldwide export and consumption also has increasingly far-reaching consequences. These risks—which were explored in-depth in a recent Forum workshop summary report entitled Addressing Food-borne Threats to Health (IOM, 2006)—are illustrated by recurrent outbreaks of foodborne illnesses traced to imported produce, Tauxe noted. To address this situation, Tauxe suggested that companies importing produce into the United States should be compelled to meet water quality standards “both in the packing sheds and in the workers’ homes.” Yet, in light of recent foodborne disease outbreaks linked to produce grown in the United States—spinach laced with E. coli O157:H7 (Calvin, 2007) and Salmonella in alfalfa sprouts (CDC, 2009)—coupled with the observation that “sanitary standards at U.S. food production facilities are vastly inferior to others in foreign sites” (Osterholm, 2006), it appears that more stringent domestic water quality standards and improved sanitary standards at food production/processing facilities may also be in order (see Tauxe in Chapter 4 and IOM [2006]).

Lessons from Waterborne Disease Outbreaks in the Americas

The following three case studies comprised a workshop session that focused on connections between climate and weather, human demographics, land use, infrastructure, and infectious disease outbreaks. Each presentation featured an outbreak chronology, an analysis of contributing factors, and a consideration of lessons learned (see Chapter 2).

Cholera in Peru, 1991

Cholera, a diarrheal disease caused by Vibrio cholerae that is endemic to the Ganges Delta in India, has also emerged in seven distinct pandemic waves since the early 1800s (Figure WO-10). When cholera reemerged in the Western Hemisphere in 1991, after being absent for more than a century, it first appeared in Peru. There, three simultaneous outbreaks in three coastal cities produced hundreds of thousands of cases in a matter of months (Seas et al., 2000), igniting an eight-year epidemic that spread across South America. In his workshop presentation, Forum member Eduardo Gotuzzo of the Universidad Peruana Cayetano Heredia in Lima, Peru, described social and environmental contributors to the epidemic, the public health response (in which he played a leadership role), and the potential use of early warning systems, based on environmental conditions, to anticipate future cholera outbreaks (see Seas and Gotuzzo in Chapter 2).

FIGURE WO-10. The seventh cholera pandemic.

FIGURE WO-10

The seventh cholera pandemic. SOURCE: Carlos Seas. Cólera. Medicina Tropical. CD-ROM. Version 2002. Instituto de Medicina Tropical, Príncipe Leopoldo. Amberes, Bélgica. (more...)

Cholera arrived in Peru during a time of hyperinflation, political unrest, episodes of terrorism, and high rates of unemployment, Gotuzzo recalled. Water quality was poor throughout the country and especially in rural areas, where sanitation coverage reached only about one in five people. As the number of cases mounted, epidemiological investigations revealed a number of underlying risk factors for infection, all of which would be expected to raise the risk of water- or foodborne infections via the fecal-oral route: having a family member with diarrhea, consuming water and food from street vendors, and being unemployed (a marker for poverty). Orders to boil water were issued, street vending of food and drinks was prohibited, and consumption of the national dish, ceviche (seafood “cooked” with acidic juices, rather than with heat), was prohibited. The rapid establishment of free treatment centers, where cholera victims received oral and intravenous rehydration therapy, helped to prevent high mortality rates, Gotuzzo noted.

Public health officials also investigated the presence of V. cholerae in the environment and were able to detect the pathogen’s presence in communities before the first human cases appeared, Gotuzzo said. Subsequent investigations of the complex, climate-dependent relationship between V. cholerae and the zooplankton species that serve as its reservoir host, as depicted in Figure WO-11, suggested that El Niño conditions, which increase sea surface temperatures, raised the concentration of the pathogen in Peruvian coastal waters (Gil et al., 2004; Seas et al., 2000).

FIGURE WO-11. A hierarchical model for cholera transmission.

FIGURE WO-11

A hierarchical model for cholera transmission. SOURCE: Reprinted from Lipp et al. (2002) with permission from the American Society for Microbiology.

Once introduced into coastal communities in concentrations large enough for human infection to occur, cholera could have spread readily via contaminated water and food. The ability to measure sea surface temperature and zooplankton concentrations via remote sensing now enables the prediction of cholera outbreaks based on environmental conditions (Colwell, 2004; Gil et al., 2004). 23

Cryptosporidiosis in Milwaukee, 1993

While poverty and lack of sanitation coverage fueled the cholera “tsunami” in Peru and its subsequent spread across South America in the early 1990s, an epidemic of cryptosporidiosis two years later in a U.S. city, which sickened over 400,000 people and caused at least 50 deaths, demonstrated that even “modern” water treatment and distribution facilities are susceptible to contamination. This latter event resulted in a massive waterborne epidemic—the largest ever recorded in the continental United States. Developed countries bear only a fraction—about 1 percent—of the global burden of diarrheal diseases (Prüss-Üstün et al., 2008). Nonetheless, there have been several serious incidents of waterborne disease outbreaks in some of the world’s wealthiest countries, including the United States and Canada. According to the CDC, a total of 36 waterborne disease outbreaks were reported in 19 states between 2003 and 2004; 30 of these outbreaks were associated with drinking water and were estimated to have caused more than 2,700 illnesses (mainly gastroenteritis, as well as acute respiratory illness associated with water aerosols) and four deaths (Liang et al., 2006).

Like the cholera outbreak in Peru, the epidemic in Milwaukee became clear when unusually large numbers of people sought treatment for gastrointestinal illness and were absent from work and school (see Davis et al. in Chapter 2). “We felt that this was a waterborne outbreak until proven otherwise,” recalled speaker Jeffrey Davis of the Wisconsin Division of Public Health. When their initial, cursory review of local finished water quality data revealed a spike in turbidity just prior to the outbreak’s onset, they began an in-depth investigation of the city’s water works. Information on infection rates among various “fixed populations” (e.g., nursing home residents) in different locations pointed to one of the city’s two water treatment plants as the source of the outbreak, as depicted in Figure WO-12. Meanwhile, after stool samples from some patients with gastrointestinal illness (that had tested negative for enteric pathogens) were further tested for cryptosporidium and found to be positive, Milwaukee’s mayor issued a “boil water” advisory.

FIGURE WO-12. Rate of watery diarrhea from March 1 through April 28, 1993, among respondents in a random-digit telephone survey of households in the five-county Greater Milwaukee area, by Milwaukee Water Works region.

FIGURE WO-12

Rate of watery diarrhea from March 1 through April 28, 1993, among respondents in a random-digit telephone survey of households in the five-county Greater Milwaukee area, by Milwaukee Water (more...)

Davis and colleagues pursued the question of how cryptosporidium came to contaminate finished water from the city’s southern treatment plant from several angles (Mac Kenzie et al., 1994). Eventually, they concluded that the outbreak resulted from a “perfect storm” of conditions, which included the contamination of a storm sewer that emptied into Lake Michigan with animal wastes from an abattoir, record-setting rainfall while the ground remained frozen, unusual wind conditions and directions that served to funnel contaminated water toward the southern water plant’s intake grid in Lake Michigan, and inadequate removal of particulate matter due to problems associated with a change in the coagulants used in the treatment plant. Amplification of the pathogen in humans, 24 coupled with delays in diagnosing the infectious agent (due to the fact that patients with gastrointestinal illness were not routinely tested for the presence of cryptosporidium oocytes in their stools), served to intensify the outbreak and its consequences for public health, Davis explained.

Among the lessons learned from this harrowing experience, Davis noted

  • The importance of stringent water quality standards, and in particular that turbidity is more than an aesthetic property of finished water;
  • The demand for advances in water sampling that maximize safety and minimize response time;
  • The necessity of good public health surveillance for determining the scope, source, and progress of an outbreak;
  • The need for communication between public health and water authority agencies to prevent and address waterborne disease outbreaks; and
  • The critical role of the media in disseminating public health messages.

Perhaps the most enduring impact of the 1993 outbreak was increased public awareness of cryptosporidium, which at the time was a relatively novel microbial threat, and which led to improvements in disease surveillance, water testing, and enhanced water treatment. “Once these modifications were made in [Milwaukee’s] treatment facilities, people from all over the world have been visiting, looking at the changes that were made,” Davis said, “It has become very, very instructive.”

E. coli O157:H7 and Campylobacter, Walkerton, Ontario, 2000

Bacterial contamination of the water supply in Walkerton, Ontario, in the spring of 2000 sickened nearly half of the town’s 5,000 residents and caused 7 deaths, as well as 27 cases of hemolytic uremic syndrome, a serious kidney disease with potential lifelong complications (Hrudey and Walker, 2005). The outbreak also resulted in severe economic consequences for the town and province, and a loss of confidence in the public trust. As speaker Steve Hrudey, of the University of Alberta, observed, prevention of this tragedy—which occurred largely as a result of negligence, ignorance, and mendacity—was “painfully easy in hindsight.”

The outbreak began on May 18, 2000, six days after an extremely heavy rainfall (a 60-year event) flooded the area, washing manure from a barnyard into a nearby shallow well (Figure WO-13; see Hrudey and Hrudey in Chapter 2). Although this well had previously been identified as vulnerable to agricultural contamination, it was not maintained to achieve prescribed chlorination standards, nor was chlorination increased in response to the flooding event.

FIGURE WO-13. Location of Walkerton Well 5 near farms to south and west.

FIGURE WO-13

Location of Walkerton Well 5 near farms to south and west. SOURCE: Adapted from original photo taken for the Walkerton Inquiry by Constable Marc Bolduc, Royal Canadian Mounted Police.

The resulting fatal outbreak was precipitated by failures at every level of oversight, from the operators of the Walkerton water system to the government and people of Ontario—a chain of blame so long that one wondered, as Hrudey did, how 22 years managed to elapse between the well’s ill-conceived creation and its deadly outcome.

In order to find ways to prevent the occurrence of similar tragedies, Hrudey and coauthor Elizabeth Hrudey (Hrudey and Hrudey, 2007) analyzed 73 published case studies of drinking water outbreaks that occurred in 15 affluent countries between 1974 and 2007, in order to determine “what failed and why.” While each outbreak had unique features, Hrudey noted that the single most common factor was complacency among officials responsible for water safety, and indeed on the part of society at large. This in turn led to failure to recognize problems within water systems and to address conditions (such as flooding) that pose challenges to system capacity. “Prevention of future outbreaks does not demand perfection, only a commitment to learn from past mistakes and to act on what has been learned,” the authors concluded.

Water Infrastructure: Recognizing Vulnerabilities and Opportunities for Improvements

Several workshop speakers offered diverse perspectives on the multifaceted issue of water infrastructure vulnerabilities and strategies to address them. Despite the vast differences between water infrastructures in developing and developed country settings, participants acknowledged common elements underlying effective public health strategies for preventing water-related diseases.

Threats to Safe Water Availability

Drinking water distribution systems Most of the approximately one million miles of pipes that comprise the U.S. drinking water distribution system’s infrastructure are due for replacement within the next 30 years (NRC, 2006). According to presenter Michael Beach of the CDC, over the next 20 years this “routine maintenance” of the water distribution/sanitation infrastructure may cost the country between $300 billion and $1 trillion. Deficiencies in the water distribution system, according to Beach, are estimated to account for between 13 and 17 percent of all U.S. waterborne disease outbreaks. As the system’s infrastructure continues to deteriorate, such outbreaks are likely to become more frequent.

A recent report by the National Research Council (2006), Drinking Water Distribution Systems: Assessing and Reducing Risks, concluded that addressing the threat of waterborne disease associated with water distributions systems would require a greater understanding of the ecological underpinnings of these threats, as well as specifically targeted epidemiologic studies. Beach noted, however, that pathogen surveillance informed by such efforts would be limited to regulated water distribution systems within the jurisdiction of a utility and would therefore exclude the increasing numbers of wells and other small, private water distribution systems in the United States—which now serve about 12 percent of the population—as well as “premise plumbing”: pipes that lie on private property, within houses and buildings (see Beach et al. in Chapter 3).

Premise plumbing is of particular concern, according to Beach, given the rise of Legionella-associated disease in the United States, which in 2005–2006 accounted for approximately half of all reported waterborne disease outbreaks. Although the pathogen may be present at undetectable levels in public water systems, “this is a premise plumbing issue,” Beach explained. “Legionella is colonizing buildings [such as hospitals and nursing homes] and then causing disease, especially in vulnerable populations.”

Another potential, and largely uncharacterized, source of waterborne disease in the United States is recreational water 25 use. Over recent decades, Beach noted, the number of outbreaks of cryptosporidiosis and other diarrheal diseases associated with swimming pools, water parks, and other “disinfected venues” has increased dramatically. As discussed earlier, after cryptosporidiosis contaminated Milwaukee’s drinking water in 1993 (see Davis in Chapter 2), “satellite” recreational outbreaks occurred in swimming pools. Today, this pathogen is increasingly linked to community-wide outbreaks that stem from inadequate chlorination in individual swimming pools.

The measurable reduction in waterborne disease outbreaks in the United States over the past 30 years attests to the effectiveness of water quality regulations to improve public health, Beach concluded. Further improvements will require a better understanding of the circumstances surrounding current water-borne disease outbreaks, and therefore “where the gaps in regulation exist and where we need to step in again.”

Climate change effects Several phenomena associated with climate change—including extreme weather events (e.g., flooding and droughts), altered patterns of precipitation and river runoff, and decreased snow cover—are expected to present challenges to the consistent availability of safe water (IPCC, 2008). In her workshop presentation speaker Joan Rose, of Michigan State University, observed that in addition to directly affecting the size of water supplies, temperature and precipitation interact with other factors such as land use patterns to produce indirect effects on water quality through agricultural runoff and industrial pollution.

Research concerning the effects of climate on water quality tends to measure changes in three main indicators: concentrations of fecal bacteria (typically E. coli) in water supplies, the overall pathogen load present in water from various sources, and the burden of waterborne disease. In her contribution to Chapter 3, Rose describes the basis for each of these types of studies and presents examples of their findings. Among the 540 waterborne disease outbreaks reported to the CDC between 1948 and 1994, for example, about 50 percent were preceded (immediately, in the case of surface waters; after a two-month lag, in the case of ground waters) by episodes of rain that exceeded the 90th percentile for local precipitation (Curriero et al., 2001). As was previously noted, similar heavy precipitation events preceded major waterborne disease outbreaks in both Milwaukee, Wisconsin (see Davis et al. in Chapter 2) and Walkerton, Ontario (see Hrudey and Hrudey in Chapter 2). Heavy rains—as well as high winds—also preceded the widespread contamination of groundwater by sewage on South Bass Island in Lake Erie in 2005, Rose reported (see Chapter 3). Hundreds of residents and tourists were sickened by a combination of pathogens that included Campylobacter and adenoviruses.

Floods affect more people than droughts, windstorms, and geological disasters (e.g., earthquakes) combined (Hoyois et al., 2007). Floods are also associated with a range of waterborne illnesses, including diarrhea, cholera, typhoid, hepatitis, and leptospirosis, Rose noted. However, she added, because there is no widely accepted definition of “flooding,” it is difficult to estimate its contribution to the burden of waterborne disease. Flooding must also be defined so that different flooding events can be recorded and compared in order to make actionable predictions of future risks to vulnerable water supplies in advance of climate variations such as El Niño, Rose said.

Disease Surveillance and Pathogen Detection

U.S. waterborne disease surveillance The spectrum of waterborne diseases in the United States, as described in Box WO-3, derives from reports made by local health departments to the CDC’s Waterborne Disease and Outbreak Surveillance System (WBDOSS). Due to the passive nature of this surveillance, and its inability to track endemic waterborne disease, WBDOSS registers only a fraction of the true burden of disease associated with water exposure, Beach said. He noted that estimates of the actual number of acute gastrointestinal illnesses associated with public water supplies range from 4 to 33 million cases per year (see Beach et al. in Chapter 3).

Box Icon

BOX WO-3

Spectrum of Water-Related Disease in the United States. Acute gastroenteritis Cryptosporidium, toxigenic E. coli, Giardia, Shigella, norovirus, chemicals

Pathogen monitoring In the United States, pathogen monitoring is generally limited to water treatment facilities, where measures such as fecal and total coliform bacterial counts are used to gauge treatment efficacy. Not only do these methods fail to detect a broad spectrum of human pathogens (including some known to resist standard treatments), they also miss microbes that enter the distribution system beyond the treatment plant, such as when floodwaters breach distribution systems or when deteriorating pipes allow contaminated groundwater to enter the drinking water supply, according to workshop presenter Kelly Reynolds of the University of Arizona (see Reynolds and Mena in Chapter 3).

In order to evaluate these inconsistencies, while avoiding the logistical difficulties associated with “testing at the tap” in private homes and businesses, Reynolds and coworkers examined pathogens present on filters in water vending machines (Miles et al., 2008). Twenty-seven percent of the 45 filters, which were not specifically designed to trap pathogens, tested positive for total coliform bacteria, including several fecal indicator species, suggesting that contamination had occurred post-treatment. The investigators also identified several types of culturable viruses. Reynolds advocated more extensive real-time monitoring in order to survey exposure to waterborne disease, as well as long-term analyses to determine exposure levels for different populations.

Water testing The United States, like many other industrialized countries, does not routinely require drinking water testing for the presence of specific microbial contaminants, according to speaker Mark Sobsey of the University of North Carolina at Chapel Hill. While more accurate and comprehensive water testing could reduce waterborne disease risks in industrialized countries, testing is essential to providing safe water in developing and developed countries. In these settings, water quality data are needed to select promising sources for drinking water and appropriate treatments to ensure its safety, as well as to classify existing sources for the purposes of studying their health effects. Unfortunately, Sobsey observed, most water tests are not accessible, too complicated, or too costly for routine use in developing countries.

The “ideal” water test for microbial contamination in low-resource settings would be low cost, portable, self-contained, lab-free, electricity-free, and globally available, Sobsey said. It would also support data communication and serve as a tool for educating and mobilizing stakeholders, especially youth, to improve public health. Tests currently being developed to achieve these goals include a variety of culture methods for E. coli and other pathogens that can be conducted at ambient temperatures, or which contain internal temperature controls (see Chapter 3). Sobsey went on to predict that culture-free and direct methods for detecting waterborne pathogens would predominate in the future.

Risk Assessment

Estimates of the true impact of waterborne disease vary widely because they rely on extrapolations of exposure, rather than on surveillance based on accurate monitoring and testing of pathogens in the water supply, Reynolds observed. She noted that risk assessments for water-related diseases are also hampered by the dearth of epidemiological data on pathogen infectivity rates and dose responses, particularly in vulnerable populations such as infants, immunocompromised individuals, and the elderly.

Notwithstanding these limitations, Reynolds and coworkers have used mathematical modeling techniques and a predetermined standard of “acceptable risk” to evaluate various pathogens in water supplies (see Reynolds and Mena in Chapter 3). “In a particular water source, we can evaluate either the level of pathogens that can be present to meet the acceptable risk level, or which treatment measures need to be initiated to meet [the defined acceptable risk level] at the point of consumption,” Reynolds explained. Through an iterative process, the models’ plausibility is judged against epidemiological data, while the modeled risk estimates can be used to target future epidemiological studies. According to Reynolds, it is currently possible to make “reasonable assumptions” about how to extrapolate disease risk to different populations at different levels of exposure to waterborne pathogens. Rose insisted, however, that accurate exposure and dose-response measures could only be obtained from animal models and properly designed and conducted outbreak investigations.

The risk modeling process also provokes further questions, Reynolds observed, including

  • What is our goal of acceptable risk?
  • What is the realized risk?
  • How bad is exposure to these different types of organisms or a mixture of these organisms? Can we evaluate that?
  • What are our risk-reduction potentials?

Water Treatment

Methodology Despite his emphasis on the importance of water testing, Sobsey—along with other participants at this workshop—indicated that, given limited resources, it may be better to treat and protect water first, then test if possible to ensure that the treatment was effective. But, as his University of North Carolina colleague Philip Singer made clear in a presentation he called “Sanitary Engineering 101,” determining the “best” treatment regime for a given water supply is far from simple (see Singer in Chapter 4). Having reviewed a broad range of disinfectants, Singer focused on the use of chlorine, describing water quality factors including reduced inorganic material, dissolved organic carbon, and microbial contents that must be addressed in order to achieve disinfection by this method. Singer also discussed the parameters and limitations of various approaches to water treatment, emphasizing the significant barriers to disinfection posed by particulate matter and describing different methods and approaches for its removal by filtration and flocculation. 26

Effectiveness and cost-effectiveness Based on a systematic review of intervention trials to improve microbiological water quality levels at both source (dug wells, boreholes, or stand posts) and point of use (improved storage, chlorination, solar disinfection, filtration, or combined flocculation-disinfection using a water-purifying product) for their ability to prevent diarrhea, Clasen and coworkers (Clasen et al., 2007b; see Chapter 4) concluded that all were effective for preventing diarrhea in children younger than five years of age, but were inconsistent in their effectiveness for reasons unexplained by research. For example, filtration appeared to be more effective than other methods in preventing diarrhea, but this difference could not be attributed to its ability to remove microbes from water. Instead, Clasen suggested, filtration may have been used more routinely than other methods due to its superior ability to improve how water looks, tastes, and smells as compared with other disinfection methods such as chlorination or solar (ultra-violet [UV]) exposure.

Given this result, Clasen’s group conducted a cost-effectiveness analysis to determine the cost per disability-adjusted life year (DALY, a measure of disease burden) averted for a similar range of interventions against diarrhea at the water source as well as chlorination, filtration, solar disinfection, and flocculation at the household level (Clasen et al., 2007a). “These aren’t cost-benefit analyses,” he explained. “We aren’t looking at improvements in productivity . . . we are just looking at . . . actual savings from health care expenditures as a result of reduced diarrheal disease.” The researchers found that, upon reaching 50 percent of a country’s population, interventions involving household chlorination and solar disinfection paid for themselves, and that all interventions were cost-effective.

Scaling up household water treatment and storage interventions Among the various definitions of “scaling up,” Clasen has chosen the most expansive to describe efforts to increase the availability, uptake, and correct, consistent use of household water treatment and safe storage systems (Clasen, 2008). These efforts are spearheaded by the International Network to Promote Household Water Treatment and Safe Storage, a consortium of interested UN agencies, bilateral development agencies, international nongovernmental organizations, research institutions, international professional associations, and private sector and industry associations (WHO, 2008d).

Presently, only a tiny fraction of the millions of people who could benefit from household water treatment and safe storage interventions—far more than the nearly one billion who use “unimproved” water sources—are being served, and those who need them most are the most difficult to reach. This uptake problem is not restricted to safe water initiatives, Clasen added: it is common to a host of public health interventions targeting individual households, including oral rehydration salts, insecticide-treated bed nets, and improvements in sanitation services. Examining uptake successes for other such products, Clasen discussed several initiatives that are currently being employed to boost public acceptance and use of household safe water and storage (see Chapter 4). Prominent among these strategies is the promotion of nonhealth benefits such as cost saving, convenience, and aesthetic appeal. Clasen also noted several challenges to these efforts, including the popular notion that diarrhea is not a disease, but merely an annoyance—or worse, a way to purify one’s body.

Water Access

Solutions for the developing world As Kolsky and coauthors observe in Chapter 4, “water access at the household scale is critical to increasing the quantity of water used to improve hygiene . . . [but] the perspective of the service provider . . . is often different from that of the householder and the public health specialist. . . . The highest priority of the water engineer is often the intake and central treatment works. Their attitude is, if this link in the chain fails, the rest will fail” (Bostoen et al., 2007). While this engineer’s worldview largely defines water infrastructure in the industrialized world, according to workshop speaker Joseph Hughes, of the Georgia Institute of Technology, it represents a barrier to solving water needs in developing countries.

Hughes described the diverse and complex elements of the U.S. civil water system, which range from water supply creation to resource protection to the “heavy infrastructure” of treatment plants and systems for water conveyance, storage, and the management of residual (post-treatment) waste (see Caravati et al. in Chapter 4). “We have a system that is poorly translatable” to the developing world, he concluded. “So if the system won’t work where we need it, we need a new system.” He proceeded to describe small, distributed, simple solutions, as well as technologies that lie somewhere between the disparate ends of the spectrum currently occupied by the developing (low-tech) and industrialized (high-tech) worlds. “Functionally we have nothing in the middle [of this spectrum] right now,” he observed, “and certainly no research.”

While acknowledging the many and formidable barriers to innovation under these circumstances, Hughes offered several reasons for optimism. Over recent decades, he noted, the combined efforts of engineers and medical researchers have vastly advanced medical instrumentation; they could do the same for safe water technologies. As the growth of distributed energy systems reduces energy costs to levels supportable by microfinance, more people will be able to invest in small-scale infrastructure appropriate to the developing world, he added. Microfinancing can also support businesses based on safe water or sanitation, such as the use of fecal matter to generate electricity. With little more than “a piece of wire and two pieces of cloth—[and] the bacteria [present in] feces—you can make electricity,” Hughes said. “Not enough to light up a city, but you can charge a lot of cell phones.”

Successful development of innovative solutions for water and sanitation in developing countries will require careful attention to matters of scale, Hughes continued. These extend from the rate and area of deployment of an intervention—in the form of a product or service, governed by a business plan—to educational requirements necessary for its implementation. “There is technology being developed all over the world . . . that could be brought into the [water and sanitation] sector if there is a business opportunity,” he concluded.

The toilet-to-tap conundrum As previously noted herein, and highlighted in Running Dry (Thebaut, 2005; see enclosed DVD), water supplies—as depicted in Figure WO-14, which shows the consumption of water in the United States as compared to other countries—are becoming increasingly limited. Drought conditions that have exacerbated pressure on dwindling freshwater resources in the southeastern United States and the Colorado River basin have encouraged development of systems for wastewater reuse, Beach said, including so-called “toilet-to-tap” renewal (see Beach et al. in Chapter 3). This is a misnomer, he added, because the majority of water consumed in U.S. households is used for cooking and bathing.

FIGURE WO-14. Water consumption in the United States compared with other countries.

FIGURE WO-14

Water consumption in the United States compared with other countries. SOURCE: Courtesy of Data360, http://www.data360.org/dsg.aspx?Data_Set_Group_Id=757 (accessed June 4, 2009).

We need to investigate the health effects associated with such increasingly necessary adaptive strategies for water scarcity, Beach advised. Understanding how to use different grades of water safely will help to address potentially conflicting needs for water quality and quantity.

Improving Sanitation. Diarrhea—usually caused by feces-contaminated food or water—kills a child every fifteen seconds. That means more people die of diarrhea than all the people killed in conflict since the Second World War. Diarrhea, says the UN children’s agency UNICEF, is the largest hurdle a small child in a developing country has to overcome. Larger than AIDS, or TB, or malaria. 2.2 million people—mostly children—die from an affliction that to most westerners is the result of bad takeout. Public health professionals talk about water-related diseases, but that is a euphemism for the truth. These are shit-related diseases (George, 2008).

A gram of feces can contain 10 million viruses, 1 million bacteria, 1,000 parasite cysts, and 100 worm eggs; one sanitation specialist has estimated that people who live in areas with inadequate sanitation ingest 10 grams of fecal matter every day (George, 2008). Perhaps it is not surprising, then, that approximately 80 percent of the world’s illness is caused by fecal matter 27 (George, 2008). As Kolsky, of the World Bank, wryly observed, it is a frequently overlooked truth that drinking clean water does not entirely protect us from the “fecal peril.” Fluids are but one route of invasion for fecal pathogens; as shown in Figure WO-15, sanitation and hygiene are necessary to close the others.

FIGURE WO-15. The “F” diagram.

FIGURE WO-15

The “F” diagram. SOURCE: Reprinted from Bostoen et al. (2007) and based on Wagner and Lanoix (1958) with permission from the World Health Organization.

Yet health is not high on the list of reasons why people want sanitation, Kolsky reported. More often, they want privacy and dignity, and to avoid flies and foul odors. Moreover, he noted, even if public health improves following a sanitation intervention, its success or failure is likely to be judged on its reliability—how often breakdowns occur—compared to its cost. Be that as it may, any enticements to sanitation should be seized upon to “sell” interventions that ultimately benefit public health, Kolsky concluded.

Investment, Implementation, and Entrepreneurship

Investment and implementation: The World Bank perspective A deep financing gap separates investments needed for water and sanitation infrastructure and actual spending, according to speaker Vahid Alavian, of the World Bank. As Alavian observed, an estimated annual global investment of $25 to $30 billion in water and sanitation is necessary for meeting the MDG, but the world is spending only about half that amount.

As the largest global investor in water and sanitation, the World Bank follows a two-pronged approach, financing water and sanitation interventions that are intended to benefit either the entire economy of a nation or its poorest citizens. In either case, the bank focuses on the long term, supporting sustainable efforts to address endemic disease in developing countries, Alavian explained. This commitment requires not only financial resources, but also support for scaling up and expanding interventions, strengthening governance and institutions, and ensuring sustainability. In Senegal, for example, before financing the recovery of a water utility from bankruptcy, the World Bank established capacity-building and sector reform to create a viable environment for their later investment. As a result, the bank’s relatively small contribution of about $500 million was leveraged into interventions that are likely to enable the country to meet the water and sanitation MDG, Alavian reported.

Since people invest in water and sanitation primarily for reasons unrelated to health, and therefore health improvement is not a priority for the design, construction, and operation of water supply and sanitation infrastructure, the World Bank must determine how to make investments in such projects as beneficial as possible from a public health standpoint, Kolsky said. This already difficult challenge is further complicated by the differing agendas of various sectors (e.g., health, urban development, utility, environment) involved in water and sanitation (see Boeston et al. in Chapter 4). Kolsky maintained, however, that when incorporated into water and sanitation projects from their inception, health interventions are relatively inexpensive to implement. Kolsky concluded, therefore, that “we need to build our public health perspective early on in project design, and we need to think about water and wastes and behavior.”

Kolsky described one example of such a design process, which resulted from the discovery by an urban planner in India that plans to construct water infrastructure to serve a city center involved laying pipes through a slum area. Based on his determination that the cost of connecting the slum neighborhoods to the planned sewer and water network was negligible relative to the overall expense of the project, the planner was able to convince government officials to extend the benefits of the new network to the city’s poorest residents.

Social entrepreneurship Much as distributed energy systems and micro-financing encourage the development of small-scale solutions for water and sanitation in developing countries, social entrepreneurship can provide the impetus for communities to use these tools to address their particular public health needs, explained speaker Sharon Hrynkow of the National Institute of Environmental Health Sciences (NIEHS).

Through a series of examples—ranging in scale from an NIEHS Superfund 28 basic research program on the remediation of arsenic-tainted wells in India to a community-run pay toilet organization in Indonesia—Hrynkow illustrated the tenets of social entrepreneurship as they apply to the development of water and sanitation interventions (see Chapter 4). Instead of viewing communities simply as beneficiaries of received services, a social entrepreneur recognizes a collection of experts who can judge the appropriateness of interventions and sustain successful ones, she said.

This perspective, which is not shared by medical researchers, offers a means to better understand why certain communities accept and develop new technologies, Hrynkow observed. To gain this perspective, she recommended that public health practitioners work more closely with social entrepreneurs (“we can put them on our boards, in our public slots; we can link them to our researchers on the ground in foreign countries”) and use their ideas and enthusiasm to engage the next generation of public health researchers.

Needs and Opportunities

Central Themes

Over the course of the two days of this workshop, discussions returned to three main themes that underlie needs and opportunities for reducing the burden of water-related infectious diseases. The distillation of these discussion “themes” inform subsequent, specific considerations described below regarding the research agenda, opportunities for public heath intervention, infrastructure development and improvement, and strategic approaches to addressing issues in water, sanitation, and health. They are not, nor should they be interpreted to be, conclusions or recommendations arrived at through a deliberative consensus study process.

Global phenomena, local effects While the global water crisis may be viewed as a byproduct of interdependent global phenomena that includes population growth, industrialization, climate change, and urbanization, its impact on public health is locally variable, necessitating local solutions. Ecological factors contributing to infectious disease emergence are particularly influential in the case of water-related diseases.

Route and scale Each of the various water-related disease transmission processes can be interrupted at multiple points, permitting intervention on a range of geographic scales. Effective water and sanitation infrastructure is both appropriately scaled and sustainable for a given setting.

Human behavior From the implementation of individual interventions, to the resolution of border conflicts over water access, to international cooperation necessary to avert a global water crisis, success depends upon human actions and interactions motivated by diverse factors, of which a scientifically sound assessment of risk and benefit is but one.

Interventions to Address Water-Related Diseases

Interventions to improve health by increasing water quality, sanitation, and hygiene can be implemented at many points throughout the water distribution system, from source to household to consumer. As discussed by Clasen and Cairncross (2004), these interventions include the following:

  • source water protection;
  • removal of pathogens by physical methods (e.g., filtration, adsorption, and sedimentation), chemical treatment (e.g., assisted sedimentation, chemical disinfection, and ion exchange), or heat and UV radiation;
  • maintaining the microbiological quality of safe drinking water through piped distribution, residual disinfection, and improved storage;
  • steps to encourage proper disposal of human feces;
  • increased access to and availability of safe water; and
  • hygienic practices within domestic and community settings, such as handwashing.

Convenient access to “improved” water in quantity encourages better hygiene and limits the spread of diarrheal disease. Diarrheal disease morbidity may also be dramatically reduced by relatively simple interventions, as illustrated in Figure WO-16 (Cairncross and Valdmanis, 2006; WHO/UNICEF, 2005). Placing a water tap close to a home nearly doubles the odds of a mother cleaning her hands after contact with fecal material from a child. Poor women who spend hours per day collecting water usually view the time-saving aspect of an improved water supply as its greatest benefit. Similarly, access to even basic forms of improved sanitation, such as pit latrines, helps prevent exposures to diseases such as diarrhea, intestinal worm parasites, and trachoma. This outcome may result from improved hygiene practices that accompany better sanitation, which are also associated with social advantages such as higher status in the community, safety, convenience, and privacy.

FIGURE WO-16. Reduction in diarrheal diseases morbidity resulting from improvements in drinking water and sanitation services.

FIGURE WO-16

Reduction in diarrheal diseases morbidity resulting from improvements in drinking water and sanitation services. SOURCE: Based on data in Fewtrell et al. (2005), and reprinted from WHO/UNICEF (more...)

In areas where the water supply is adequate, the adoption of simple and inexpensive methods to improve the microbiological quality of existing water supplies can significantly mitigate the disease burden due to diarrheal diseases. Many point-of-use interventions, such as filtration, disinfection with radiation, boiling or chlorine, or simply the provision of enclosed, protected containers have been shown to be effective (interestingly, the use of a combination of methods simultaneously was not shown to have any added benefit; Clasen et al., 2006; Fewtrell et al., 2005). However, any intervention or provision of clean water and sanitation will only be successful if it is used. Education of the population, as well as considerations of cost, accessibility, and acceptability of interventions, will be key issues in the design and implementation of these interventions.

According to the second edition of the report Disease Control Priorities in Developing Countries (Cairncross and Valdmanis, 2006), the main health benefit of water supply, sanitation, and hygiene is a reduction in diarrheal disease. However, the effect on the incidence and prevalence of other diseases, such as dracunculiasis, schistosomiasis, and trachoma, is substantial. Water, sanitation, and hygiene improvements could eliminate 3 to 4 percent of the global burden of disease (Cairncross and Valdmanis, 2006).

Sustained interventions to reduce vector-borne diseases fall into three main categories (Prüss-Üstün et al., 2008):

  • Modifying the environment to permanently change the land, water or vegetation in ways that reduce vector habitats such as drainage, leveling land, contouring reservoirs, and altering river boundaries;
  • Manipulating the environment to create temporary (and often repeated) unfavorable conditions for vector propagation by such means as removing aquatic plants that shelter mosquito larvae, alternately flooding and drying irrigated paddy fields, periodic flushing of natural and human-made waterways, and the introduction of predators, such as larvivorous fish; and
  • Modifying or manipulating human habitation or behavior to reduce contact between humans and vectors with barriers such as window screens and nontreated mosquito nets, as well as by removing standing water in or near the home, which provide mosquito breeding sites.

The effectiveness of these and other interventions, such as sanitation and water quality management, to reduce the burden of water-related diseases will be strongly influenced by local conditions, which must be taken into account in order to make cost-effective choices to address water-related health risks in diverse contexts (Clasen and Cairncross, 2004).

Costs and Benefits of Interventions

The estimated global economic benefits of drinking water and sanitation improvements include (Prüss-Üstün et al., 2008)

  • health-care savings of $7 billion per year for health agencies and $340 million for individuals;
  • productivity gains of nearly $10 billion per year;
  • time savings equivalent to $63 billion per year; and
  • values of deaths averted (based on discounted future earnings) of more than $3 billion per year.

Taking these gains into account, an investment of $11.3 billion per year, as required to meet MDG7 sanitation and drinking water targets, would produce a return of approximately $84 billion.

Nevertheless, responding to recent shortfalls in progress toward achieving the water and sanitation targets of the MDG7, the editors of the Lancet observed that, despite such reports, most government donations to water and sanitation initiatives have not increased, nor are foundations or organizations “lining up to give money to build toilets or to fund education programmes to teach small children how to wash their hands” (Editorial, 2006). Moreover, the editorial continued, “the health-care community also seems to have lost sight of how fundamental clean water and sanitation are to health, preferring to get involved in more directly medical interventions, such as access to drugs and vaccines. It is dangerously short sighted to pour immense time and resources into vaccinating children only for them to die a few years later from diarrhoeal illnesses.”

A Public Health Research Agenda

Workshop participants, most notably speakers Beach, Rose, Bradley, and Forum member Rima Khabbaz of the CDC, identified and discussed the following bulleted points as particularly important examples of water-health relationships that merit further exploration, including:

  • What are the infectious disease risks associated with agricultural water uses?
  • What are the direct and indirect connections between water and respiratory disease?
  • What role does handwashing play in reducing the prevalence and incidence of respiratory diseases in the developing and developed world?
  • What are the infectious disease risks associated with the unregulated components of the water distribution “system,” including but not limited to private systems (private community and individual wells) and premise plumbing?

Workshop speakers Michael Beach, David Bradley, Kelly Reynolds, and Philip Singer also discussed the need for more information on the short- and long-term health and environmental consequences associated with individual exposures to water-associated diseases as well as the health and economic impacts associated with endemic water-related diseases. In particular, presenter David Bradley—who developed the Bradley Classification Scheme for water-related diseases in the 1970s—believed that additional factors could be incorporated into his original classification scheme to include behavioral and spatial aspects of changing or modifying water sources. These factors might add additional levels of complexity to our collective appreciation of the linkages between water, sanitation, and health. It was felt by presenter Reynolds that such knowledge could inform risk assessment methods development activities, and the design and priorities placed on different intervention strategies to reduce the health and economic impacts associated with these vector- and non-vector-borne diseases.

Conclusion

Safe water and sanitation pose universal challenges for public health. While global and regional phenomena such as climate change and geopolitical shifts threaten to intensify these challenges, effective solutions demand attention to local needs and opportunities. As Running Dry hopefully suggests, “most of the water crisis issues can be solved by a coordinated, global, environmentally sensitive, humanitarian effort.”

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Footnotes

1

For a discussion about Bradley’s four categories of water-related disease (water-borne, water-washed, water-based, and water-related insect vectors), see page 18 and his paper in Chapter 1.

2

See NRC (2004a,b,c, 2005a,b,c, 2006a,b,c, 2007a,b,c, 2008a,b).

3

See NRC (2002).

4

See Running Dry DVD (enclosed) and MacPherson in IOM (2008).

5

See Davies in IOM (2009).

6

aSee NRC (1993acSee NRC (2008c).

7

bSee NRC (1993b); see also Caravati et al. in Chapter 4.

8

Speakers Mark Sobsey, Thomas Clasen, and Vahid Alavian did not submit manuscripts for this summary report. To ensure that their contributions to this meeting were captured in this summary report we have supplemented the overview section of the chapter in which their material would have appeared.

9
10

For more information on this treaty, please see http://www​.usbr.gov/lc​/region/g1000/pdfiles/mex-trety.pdf.

11

Urban Water Conference, http://www​.urbanwaterconference.be/db (accessed March 13, 2009).

12

The transparent, dome-shaped window covering the front of the eye (http://www​.stlukeseye​.com/anatomy/cornea.asp).

13

The thin, transparent tissue that covers the outer surface of the eye. It begins at the outer edge of the cornea, covering the visible part of the sclera, and lining the inside of the eyelids. It is nourished by tiny blood vessels that are nearly invisible to the naked eye (http://www.stlukeseye.com/Anatomy/Conjunctiva.asp).

14

Inanimate objects or substances that can transmit infectious organisms from one host to another.

15

Dracunculiasis, or Guinea worm disease, is the only infectious disease that is caused exclusively by ingestion of contaminated drinking water.

16

Copepods are a type of crustacean which may live in both salt and freshwater. They are one of the most abundant animals on the planet (see http://jaffeweb​.ucsd​.edu/pages/celeste/Intro/index.html).

17

Bradley has since identified a fifth category of water-related disease transmission processes—water aerosols—which transmit respiratory pathogens such as Legionella (see Chapter 1).

19

Bradley defines “persistence” as the capacity to survive outside the human body (see Chapter 1).

20

By “multiply,” Bradley is referring to whether an organism multiples in excreta or in the environment (see Chapter 1).

21

Handwashing with soap and water is important for the prevention of diarrheal disease and respiratory infections.

22

WaterGuard® is the chlorine solution made in some countries for water purification. The “safe water system” involves safe water storage combined with health education.

23

For a detailed discussion of the ecological basis of cholera epidemiology, see the recent Forum workshop summary, Global Climate Change and Extreme Weather Events: Understanding the Contributions to Infectious Disease Emergence (IOM, 2008).

24

Following a minimal infective dose of approximately 130 cryptosporidium oocysts, humans excrete billions of oocysts per day in their stools and continue to do so after disease symptoms resolve.

25

Recreational water is that which is used for water-based activities in marine, freshwater, hot tubs, spas, and swimming pools (Pond, 2005).

26

The separation of a solution. Most commonly, flocculation is used to describe the removal of a sediment from a fluid. In addition to occurring naturally, flocculation can also be forced via agitation or the addition of flocculating agents. Numerous manufacturing industries use flocculation as part of their processing techniques, and it is also extensively employed in water treatment (http://www​.wisegeek.com​/what-is-flocculation.htm).

27

Approximately 80 percent of all diseases and more than a third of the deaths in developing countries are caused by the consumption of contaminated water, and on average up to a tenth of the productive lifetime of each person is taken up by water-related diseases (UNDESA, 1992).

28

Superfund is the U.S. government’s program to clean up the nation’s uncontrolled hazardous waste sites. For more information, see http://www​.epa.gov/superfund/.

Copyright © 2009, National Academy of Sciences.
Bookshelf ID: NBK28449

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