Water Safety: Reducing the Infectious Disease Burden Due to Unsafe Water, Sanitation, and Hygiene

An Expert Interview With Omar A. Khan, MD, MHS

Linda Brookes Good, MSc


December 30, 2009

Editor's Note:

The theme of the recent American Public Health Association (APHA) annual meeting, held November 7-11, 2009, in Philadelphia, Pennsylvania, was "Water and Public Health: the 21st Century Challenge." Water is necessary for all forms of life, and the demands for it are increasing. The ability to provide or the failure to provide and maintain a supply of safe and clean drinking water affects numerous aspects of society, including the health of its individuals, its ecosystems, and its economy. In the United States, as the APHA pointed out, a vast number of utility workers, scientists, sanitarians, engineers, government officials, and many others work around the clock to provide safe and clean drinking water to America's homes and businesses. Worldwide, however, 884 million people do not have access to an "improved" water source, eg, water supplied through a household connection, public standpipe, borehole well, protected dug well, protected spring, or rainwater collection.[1] An estimated 2.5 billion people lack access to adequate sanitation (more than 35% of the world's population).[2,3,4,5] The latest estimates from the World Health Organization (WHO) placed unsafe water, sanitation, and hygiene among the leading global risks for death, responsible for 1.9 million deaths and 64.2 million years of life lost as a result of premature death or illness and disability (disability-adjusted life years) in 2004.[6] These numbers represent 3.2% of all deaths and 4.2% of all disability-adjusted life years, respectively.

According to the WHO, around 10% of the total burden of disease worldwide could be prevented by improvements related to drinking water, sanitation, hygiene, and water resource management. The latest estimates link unsafe drinking water, inadequate availability of water for hygiene, and lack of access to sanitation with about 88% (1.5 million) of deaths from diarrheal diseases (including cholera, typhoid and dysentery) in children younger than 5 years of age. Unsafe water, inadequate sanitation, and insufficient hygiene are also associated with 2 billion nematode infections, 200 million cases of schistosomiasis, 0.5 million cases of malaria, as well as outbreaks of dengue, Japanese encephalitis, and onchocerciasis.

Outbreaks of disease caused by unsafe water remain comparatively rare in North America, but physicians may become complacent about the dangers of waterborne pathogens. However, several recent outbreaks of waterborne infections have occurred in the wake of disasters. Altered patterns of rainfall and increased frequency of extreme weather events are likely to influence the incidence of waterborne gastrointestinal and respiratory diseases in North America and elsewhere.

In this interview, Omar A. Khan, MD, MHS, spoke with Linda Brookes, MSc, for Medscape, to discuss water safety with respect to waterborne infections, how they affect health in developing countries, and how developed countries should become more aware of how to prevent and treat these diseases. Dr. Khan, a member of the Advisory Board for Medscape's Public Health & Prevention is a leading authority on global health and family medicine.

Medscape: The term "water safety" presumably means different things in different places; would you agree?

Dr. Khan: I would say that "water safety" as an overall term really should include all of what water can do that might be potentially harmful, and that includes, in the broadest interpretation, environmental issues like drought, and diseases (such as malaria) for which water is simply a medium for organisms to reproduce- although the water itself does not cause any problem. The WHO includes malaria as one of its water issues because the malarial larvae need stagnant water to hatch, and if you eliminate stagnant water, you reduce the number of mosquitoes carrying either dengue fever or malaria. So a broad interpretation allows us to link those other conditions with water, which might otherwise be missed.

Medscape: The theme of the APHA conference was global, but it is an American organization, so how much concern is there about water safety in the United States?

Dr. Khan: In the United States, I think that we tend to think less of water as a mode of spreading disease because, generally, we have quite good municipal water safety systems. Where I live, our municipality regularly issues a water safety report on the basis of tests for 10 elements or compounds in samples of our town water to ensure that these substances remain below allowable limits. Most people in the United States seem to care about polychlorinated biphenyls, lead, and, to some degree, fluoride. In my locality, many people worry about lead in the water. As a US-based physician, a lot of parents ask me, should my child be tested for lead? In a city like Karachi (Pakistan), however, lead is the least of the concerns; there you are concerned about getting sick and dying from drinking 1 cup of infected water, such is the level of bacteria. So, what they are concerned about in New York City is different from what they might worry about in Karachi.

Medscape: The risk in Karachi would be almost exclusively related to infections?

Dr. Khan: Yes, contracting an infection and dying either of the infection itself or of the sequelae thereof. People die of malnutrition because they experience so much vomiting and have so much diarrhea that they do not have enough time to replenish food and water. So, diarrhea, for example, is responsible for 1.5 million deaths in children each year (nearly 1 in 5 deaths in children) worldwide.[7] In the United States, in a typical week, I might see 2 cases of diarrhea a week, which is not insignificant, and of course I am going to think about all the ways that they could have acquired this diarrhea. So, in that sense, I am involved with waterborne infections in the United States. I also do travel medicine, so if someone returns from, say, Venezuela, and says he or she has diarrhea, that person is very different from an 80-year-old in a local nursing home who was recently on antibiotics and who has diarrhea. I am required to think about all of the possibilities. Much of my current medical education work involves having our medical students and residents work at our partner hospitals such as in Dhaka, Bangladesh, one of which, the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B) is the leading center for waterborne disease research in the world. The researchers there have done an extensive amount of cholera research. They developed an oral rehydration therapy in the 1960s[8], before the WHO, and they developed a cholera vaccine (Dukoral®).

Diarrheal disease, specifically infectious diarrheal disease, is the greatest worldwide threat from poor water, and more specifically I would say that the most severe diarrheal diseases would be cholera, typhoid, and various forms of dysentery, including enterohemorrhagic Escherichia coli, which can cause severe bloody diarrhea. Clearly, North America and, to some extent now, Central and South America and Europe are the most protected against diarrheal disease simply because they have better sanitation and more education. The worst hit areas are typically South Asia and sub-Saharan Africa for different reasons. In South Asia, there is a lot of mixing of water types, for example, because of the geography of Bangladesh, which is a low-lying country formed by a delta plain at the confluence of 3 rivers, drinking water there very quickly gets contaminated with sewage. Sub-Saharan Africa is affected more, simply because the other health indicators and the health infrastructure are so poor. The risk of dying from diarrheal disease is also increased because of the high rates of malnutrition and high numbers infected with HIV, in whom diarrhea becomes more frequent and severe as the immune system deteriorates. Of course, access to treatment differs also. You can get sick from cholera in America and get treated successfully very quickly. You can get sick with cholera in Bangladesh, and it will take quite a bit longer to get treated. If you get sick in sub-Saharan Africa, however, you might die. That is the issue.

Improving water safety would also prevent the several billion nematode infections that occur worldwide.[2] These include diseases of the small intestine, such as hookworm (Ancylostoma duodenale/Necator americanus) and ascariasis, an infection caused by Ascaris lumbricoides, a large roundworm. Nematodes cause morbidity but probably not as much death, although they can cause slow death by malnutrition and anemia. Nematode infections do not cause as much mortality per capita as, for example, cholera. For every 10 cholera infections, there might be 2 deaths, whereas for every thousand intestinal nematode infections, there might be 2 deaths. That may be an exaggerated difference, but it is meant to show the order of magnitude of difference between the 2 types of infection.

Medscape: Recently, the WHO identified 5 leading risk factors -- childhood underweight, unsafe sex, alcohol use, high blood pressure, unsafe water and sanitation -- as together responsible for one quarter of all deaths in the world and one fifth of all disability-adjusted life years. The WHO calculated that reducing exposure to these risk factors would increase global life expectancy by nearly 5 years.[6] Some of these risk factors can be dealt with on a one-to-one basis, but how do we improve the water?

Dr. Khan: It would be possible to achieve a one-third reduction in diarrheal disease frequency with any of the following interventions: hygiene, sanitation, water supply, and water quality. Simple handwashing with a soap solution after coming into contact with infected material cuts diarrhea frequency by one third.[9] Sanitation is a more difficult challenge, but having latrines where the sewage does not interfere with the drinking water supply will immediately reduce that community's diarrhea frequency by about one third. Constructing water supply facilities will also cut diarrhea by about one third, but that is one of the more difficult structural problems to address. Of course, cleaning the water will help, so if the government or some agency puts in tube wells or pumps that provide clean water, that would produce another one-third reduction. Improving water quality by water purification such as boiling or chlorination will reduce disease by a third as well. Very simple interventions will produce very large reductions in the frequency of diarrheal disease. So, the question is, where should one put the money? In a sense, you can put it almost anywhere in the above categories, and it will make a difference, and different communities need different things. Some communities might have a tube well, but they do not have a container to carry the water to their homes, so they have a great supply but poor quality. Or they have good supply and have good quality, and yet they are not practicing handwashing adequately; that would be a hygiene issue.

The most important issues in sub-Saharan Africa are different from the ones in South Asia. In much of South Asia, the issue is not water supply -- there, the problem is "water, water everywhere, nor any drop to drink." The quality of the water is fairly poor, however, because it gets contaminated very quickly. It has been suggested that rainwater might be used rather than trying to collect water from the ground, which might also be contaminated. So, in South Asia, it is a quality issue, whereas in Africa, it is a supply issue. Where do you get the water to begin with? In Africa, they do not have enough water, and when they do get enough water, it tends to be of fairly poor quality. I think in Africa we need to set up a network of supply systems. In South Asia, I would focus on improving water quality.

Medscape: How is this sort of thing set up? Which organizations are most involved?

Dr. Khan: The WHO takes an explicitly normative view of areas related to population health, ie, it sets norms and defines standards for issues such as clean drinking water. Among the individual organizations, The United Nations Children's Fund (UNICEF) and the Geneva-based Water Supply and Sanitation Collaborative Council (WSSCC) launched their "Water, Sanitation and Hygiene (WASH; now WASH-Plus)" campaign in 2006. The campaign uses a variety of interventions to improve the water and sanitation situation in developing countries. In 2008, UNICEF performed WASH activities in more than 100 countries.[10] WASH focuses on working with local nongovernmental organizations to implement hygiene promotion, water quality testing, emergency programs, community support, and education. It also seeks to influence policy at the national level. Nongovernmental organizations around the world have been attempting to change water policy decision-making and are granting funds for projects to improve drinking water, sanitation, and hygiene.

Medscape: Once these initiatives are up and running, how are water supplies monitored?

Dr. Khan: In the United States, this happens in 2 ways. One is, of course, at the point of contact or use, which is the water supply itself, and this can happen in water purification plants or at the faucet. The second is monitoring after the fact, which is the number of people who contract diarrhea. In the United States, for example, if someone gets diarrhea, that is not very interesting to the health department. But if I do a culture, and I detect Cryptosporidium, depending on the state, that could be a reportable diarrhea. For example, there was a big outbreak of acute watery diarrhea due to Crypto in Milwaukee, Wisconsin, in 1993, in the largest waterborne outbreak in the United States in the past 30 years.[11] We can get an estimate of what is going on with the water quality on the basis of how many people are reporting diseases.

In developing countries, monitoring is very variable. Countries with well set-up environmental protection agencies, ministries of health, and ministries of environment go out and do active surveillance. In Bangladesh, for example, people who work either for the government or for the large research centers go out and dip test tubes in water and go back into the lab and test for coliforms, cholera bacteria, etc. They also do passive surveillance, which is when people arrive at a hospital with documented cholera or diseases of that sort, the information goes into the government's or the ICDDR,B's database, and at the end of the year, they can say that we had more or less cholera than we usually do. In the United States, we do laboratory diagnosis, meaning each hospitalized person gets tested, and we can say with certainty whether the patient has cholera or some other disease because his or her stools are tested. In developing countries, however, there are so many people that it is not possible to cost-effectively test everybody, so if someone becomes symptomatic in Bangladesh during cholera season, we assume he or has cholera. In Bangladesh, when we say that someone has cholera, it is not because we made a laboratory diagnosis, it is because we made an "epidemiologic diagnosis". The way of counting people is different, but you do still end up counting people and figuring out whether cholera is increasing or decreasing.

Medscape: How realistic is it to expect improvements soon in waterborne infections?

Dr. Khan: I think that 155 years ago, when John Snow advised removing the handle of the Board Street public pump in London (when he theorized that contaminated water from the pump was the cause of cholera during the 1854 outbreak), it must have seemed very much like what we see in parts of the developing world today. London was full of plagues and poxes and diseases at that time, and there and in every other big city, many people died in their 20s and 30s from all sorts of infections and other causes that we cannot possibly imagine now. That was only a few generations ago. We have seen in our lifetimes massive improvements being made in terms of the world's water and health. Although 1.5 million children younger than 5 years of age die each year of diarrhea, and that is a lot of people, 30 years ago, we had an even higher percentage of unnecessary morbidity and mortality. So, I think we are improving; the trick is, of course, to keep going forward and recognizing the different challenges. They keep changing, but I am confident that in 100 years, we will as a scientific community look back at the time when there were so many children dying of diarrhea worldwide and at the progress we have made since then.

Medscape: Improvements have to mainly come about through prevention, right?

Dr. Khan: That is the main thing, I would say. For some diseases, we have to come up with new treatments, but there is no new diarrheal disease therapy out there on the horizon, and perhaps there won't be. There is no medicine for malnutrition, or for viral diarrheal disease, or for dengue. The medicine is prevention, and that is where, in the United States, we have made the greatest strides in hygiene and public health. The first school of public health in the United States was the Johns Hopkins School of Hygiene and Public Health in Baltimore, Maryland. It was founded more than 100 years ago with help from the Rockefeller Foundation, which named it that because hygiene improved the health status of so many people. So, that is where the biggest gains are going to come from. I am less worried about diarrhea than some other diseases like HIV, which have no cure and not even a vaccine. Interestingly, there already are some diarrheal disease vaccines, including rotavirus and cholera.

Medscape: Are new pathogens emerging, or are the old ones reemerging anywhere in the world?

Dr. Khan: Good question. I think we are seeing emerging infections. We are not seeing them in the sense that brand new disease organisms, like HIV, are evolving. We are not seeing that type of completely new disease entity in waterborne diseases. What we are seeing is what happens when human habitat, the insect habitat, and the bacterial habitat coincide. For example, if the humans decide to go into forested areas and build houses next to water sources where there may have been dengue, malaria, or Japanese encephalitis-carrying mosquitoes for hundreds and thousands of years, now it is a problem. Cities around the world were not always very crowded, so no one lived in the geographically undesirable areas where there was stagnant water. Now cities like Karachi, Mumbai, and Dhaka have expanded so much that the inhabitants take whatever patch of land they can get. So, there are many people now living next to areas of stagnant water with encephalitis-, dengue-, and malaria-carrying mosquitoes hatching just below the water's surface.

Medscape: Could global climate change affect the incidence of waterborne infectious diseases, even in areas like North America?

Dr. Khan: That has been discussed, and we do not have very much evidence for the effects of climate change yet, but we do in terms of disasters, and climate change leads to more disasters. I think with global warming, a major risk would be a greater frequency of natural disasters. To take one example, after Hurricane Katrina in 2005, Vibrio-type infections were identified in Louisiana, mainly Vibrio vulnificus, but also some cases of Vibrio parahaemolyticus, all noncholeragenic.[12] Vibrio infections were previously rare in Louisiana, but suddenly, when you had fecal matter mixing with drinking water, the entire drinking water pool became contaminated, and Louisiana was converted into Bangladesh. Bangladesh and Louisiana are geographically fairly similar in terms of how low-lying they are compared with the surrounding water areas. It is actually rather shocking how little it takes to convert a developed area into a developing area. That was the result, perhaps, of climate change and of poor planning on the part of many people. The more Katrinas we have, the more disruption of drinking water we will have, and when drinking water is disrupted, you essentially become a developing country. New Orleans became a developing country after Katrina hit, and there was water everywhere, but you could not possibly dip your hand in it and drink it because it was mixed with sewage.

Medscape: So, you are saying that waterborne infectious diseases could reemerge in other cities such as New York, if water levels rose?

Dr. Khan: The water level around Manhattan would only have to rise about 6 in, and you pretty much flood the city.

Medscape: And then the city has a water safety problem like the one you described?

Dr. Khan: Absolutely. The sea level rising is one issue because it will contaminate the water system. The other big issue is, as the weather gets warmer, the habitat may become more attractive to mosquitoes. If it does, and simultaneously there is more stagnant water, then we could potentially see a resurgence of malaria in this country, which we have not had for 30 years, or dengue, which we have never seen, except for isolated cases on the Mexican border. With warmer weather, we could have a resurgence of all mosquito-borne diseases.

Medscape: So, North America shouldn't become too complacent?

Dr. Khan: Yes, that is unfortunately how human nature works. We need something to prod us into action. For example, severe acute respiratory syndrome (SARS) almost coming to America in 2002-2003 was what made us think that we should accelerate the finalization of an influenza pandemic plan. There is an unfortunate truism in medicine that for change to happen, someone has to die. But public health works best on prevention, not by having people die and then doing something. So, it would be nice to be able to prevent all these issues, but there isn't adequate funding for a public health infrastructure in the country. Public health is largely a publicly funded enterprise, and at this point, most people are less concerned about malaria and dengue happening 30 years from now than they are about healthcare and jobs and the economy.

Medscape: But maybe they don't need to worry yet?

Dr. Khan: We are living in an interconnected world. Within about 16 hours, you can reach 85% of the points in the globe from North America. So, if someone has cholera in a faraway country, they could have cholera in New York City 16 hours later. They could have a so-called tropical diarrheal disease here. I think the point is, we have to be prepared not only to prevent but care for people who have certain illnesses at any point in time and anywhere. The sense of place is becoming less and less a valid metric of how anyone is doing. People are migratory and are moving all the time, and that sense of interconnectedness means that all of us need to care about approximately the same set of issues: If you do not care about someone else's set of issues today, they will probably be your set of issues tomorrow. So, for that selfish reason, even if we cannot convince people to be altruistic, we can at least provide some evidence of the positive aspects of acting selfishly; in this case, in one's own future self-interest.


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