New England Journal of Medicine
The first documented attempts to treat drinking water, which may date back to 4000 B.C., were recorded in Greek and Sanskrit writings that describe the boiling and filtering of water, primarily to make it smell and taste better, although reducing visible particles and turbidity was also a goal. Hippocrates invented the cloth-bag filter (or Hippocratic sleeve) and was among the first to believe that this process also rendered water more healthful for the human body. The British scientist John Snow demonstrated that the source of a cholera epidemic centered on the odorless and seemingly clean water provided by a water pump. He proved that sand filtration and chlorination effectively prevented the spread of cholera. Despite 150 years of acceptance of the healthful effects of clean water, an estimated 1.1 billion people still lack access to it, and 2.6 billion people lack access to adequate sanitation.
There are several categories of water-related disease (see table), including diarrheal diseases, skin and eye infections, and the neglected tropical diseases.3 Common waterborne diseases involve the fecal–oral transmission of a pathogen — a virus (such as hepatitis A or E or a norovirus), a bacterial enteropathogen (such as Vibrio cholerae, salmonella, enterotoxigenic Escherichia coli, shigella, campylobacter, or yersinia), or a protozoan (such as Entamoeba histolytica, giardia, or cryptosporidium). In addition, biofilms (coatings of organic and inorganic materials on water pipes) have been shown to allow the proliferation of several bacterial pathogens (including legionella and Mycobacterium avium complex) that are transmitted by inhalation, as well as of pseudomonas species and leptospira, which are transmitted by contact with skin or mucous membranes; leptospirosis epidemics have followed floods and hurricanes.
Water-based infections are those whose transmission requires an intermediate aquatic host (e.g., a freshwater snail in the case of schistosomiasis, which affects more than 160 million people). Dracunculiasis, which is transmitted to humans through copepods (water fleas) that are infected with guinea-worm larvae, is on the verge of eradication, thanks to simple cloth filtration of water combined with an education program to prevent recontamination — an effort spearheaded by the Carter Center.
Diseases transmitted by water-breeding insects that have dramatic impact on humans include malaria, dengue, yellow fever, trypanosomiasis, and onchocerciasis. The flooding and other ecologic changes associated with global climate change may alter the breeding sites for the mosquitoes, black flies, and tsetse flies that carry these diseases, affecting their incidence and distribution.
The last category of water-related disease results from water polluted by natural toxins such as arsenic or toxins introduced by industrial waste. Arsenic is found in groundwater and released by the microbial metabolism of organic material that predates modern agricultural practices in many regions. Arsenic contamination of groundwater obtained through tube wells in Bangladesh has caused the largest occurrence of poisoning in a single population.4 The contamination was discovered during the investigation of an epidemic of skin lesions that included pigmentation changes on the upper chest and keratoses of the palms and the soles of the feet (see photo). Concerns about lung, bladder, and skin cancers have prompted widespread testing and remediation efforts in Bangladesh. Arsenic contamination of groundwater has also been found in Argentina, Chile, China, India, Mexico, Thailand, and parts of the United States. Similarly, the recognition of lead contamination of pipeborne water in the United States and mercury poisoning in people who have ingested large fish that accumulate toxic levels of mercury has led to concern about heavy-metal contamination of water.
Global health issues have captured the attention of governments, global funds, and foundations. Yet most of this attention and the consequent investment have focused on diseases such as malaria, tuberculosis, and AIDS, which kill a fraction of the number of people who die from water-related diseases. The necessary political will has not been mustered to address the water and sanitation crisis, among the most neglected of the United Nations' millennium development goals. A recent cost–benefit analysis reported by the World Health Organization makes a strong case for investment in this sector, and, at its Tokyo summit meeting in July, the Group of Eight reaffirmed its commitment to addressing concerns about water.5 Political support is urgently needed at all levels for the development and implementation of evidence-based recommendations to improve access to safe water, for the enhanced surveillance of water-related diseases, for the financial support of relevant epidemiologic and laboratory research, and for the development of accessible educational materials. Clearly, we need to start talking dirty water.
No potential conflict of interest relevant to this article was reported.
Dr. Barry is a professor of medicine and public health at Yale
University School of Medicine, New Haven, CT. Dr. Hughes is a professor
of medicine at the School of Medicine and professor of global health
and senior advisor at the Center for Global Safe Water in the Rollins
School of Public Health — both at Emory University, Atlanta.
A slide presentation is available with the full text of this article at at www.nejm.org.
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