Diarrheal diseases arise through contact with feces and are spread by what is known as the fecal-oral route. Until recently, contaminated water supplies were thought to be the chief culprit, but now the pathway is known to be more complex. An even greater factor appears to be insufficient water for washing, especially hand-washing, which makes proper hygiene impossible (93). When inadequate water supplies are coupled with shared latrines – or none at all – it creates conditions rife for transmitting diarrhea. Today, an estimated 2.9 billion people lack access to adequate sanitation and roughly 1.4 billion people do not have access to safe drinking water (94). This situation has persisted despite investments of more than US$100 billion during the International Water and Sanitation Decade.
Improvements in coverage continue to be overtaken by rapid population growth and even more explosive urban growth (95)(96). Ensuring access to adequate supplies of good-quality water and some form of sanitation – coupled with hygiene education and general socioeconomic development – remain critical factors in reducing the toll of diarrheal diseases.
Diarrheal diseases are by no means limited to the developing world, although they are most deadly there. In the developed world, where diarrhea is a major cause of sickness but rarely death, Salmonella and Campylobacter jejuni, spread through tainted chicken or milk, are among the most common agents (97). In addition, new microbial agents are increasingly implicated in human disease. Campylobacter jejuni, for instance, was once found only in animals, but now it is among the most common causes of foodborne illness in humans (98). Public health officials in the United States and elsewhere warn of an epidemic of foodborne pathogens (99). Several recent outbreaks of food poisoning in the United States, Canada, Europe, and Japan have been linked with Cyclospora and a new, particularly vicious form of E. coli (100). (See Figure 1.12.) To avert any possibility of a considerable outbreak, such as occurred in Japan in 1996 from E. coli O157 (101), the U.S. Government in 1997 recalled more than 11 million kilograms of beef suspected to be contaminated with the organism (102).
In 1993, the United States experienced the largest outbreak of diarrhea in recent history – affecting more than 400,000 people – when the municipal water supply of Milwaukee, Wisconsin, was contaminated by Cryptosporidium parvum from farm animal wastes (103). This protozoan parasite has been wreaking havoc in countries across Europe as well, raising new concerns about the safety of drinking water in some of the world’s most affluent countries.
Other familiar and dangerous infectious diseases, such as cholera and hepatitis A and E, can also be transmitted by fecally contaminated food and water. This is most common in developing countries, but frequently occurs elsewhere. In the United States, for instance, 151 students and staff in four different school districts in Michigan developed hepatitis A in March 1997. The cases have been associated with the consumption of frozen strawberries imported from Mexico (104). Cholera sweeps around the globe periodically in major pandemics. Annual death rates fluctuate wildly, ranging in recent years from several thousand up to hundreds of thousands. Most deaths occur in Africa, often among displaced or refugee populations; overall, some 79 million people in Africa alone are at risk for the disease, according to WHO (105). Recent outbreaks in Latin America and the appearance of a new strain of cholera in India and Bangladesh provide examples of how changing environmental conditions can accelerate disease transmission. (See Cholera Returns.)
Among the food-, water-, and soilborne diseases, those caused by parasitic worms are noted for the debilitation they cause (106). At any one time, roughly 3.5 billion people are infected with one or several species of parasitic worms – making these among the most prevalent human infections – and some 450 million people are ill as a result (107).
References and notes
93. James Van Derslice and John Briscoe, “Environmental Interventions in Developing Countries: Interactions and Their Implications,” American Journal of Epidemiology, Vol. 141, No. 2 (1995), p. 143.
94. United Nations Children’s Fund (UNICEF), The Progress of Nations 1997 (UNICEF, New York, 1997).
95. Diane B. Bendahmene, ed., Lessons Learned in Water, Sanitation and Health: Thirteen Years of Experience in Developing Countries (Water and Sanitation for Health Project, Arlington, Virginia, 1993), p. 79.
96. Diane B. Bendahmene, ed., Lessons Learned in Water, Sanitation and Health: Thirteen Years of Experience in Developing Countries (Water and Sanitation for Health Project, Arlington, Virginia, 1993), p. 79.