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<International Source Book On Environmentally Sound Technologies
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Appendix 1
Health Effects Associated with
Wastewater and Excreta

1. Overview

The failure to properly treat and manage wastewater and excreta world-wide is directly responsible for adverse health and environmental effects. Human excreta has been implicated in the transmission of many infectious diseases including cholera, typhoid, hepatitis, polio, cryptosporidiosis, ascariasis, and schistosomiasis. WHO estimates that 2.2 million people die annually from diarrhoeal diseases and that 10% of the population of the developing world are severely infected with intestinal worms related to improper waste and excreta management (WHO, 2000a; Murray & Lopez, 1996). Human excreta-transmitted diseases predominantly affect children and the poor. Most of the deaths due to diarrhoea occur in children (accounting for nearly two million) and in developing countries (WHO, 1999a).

Infectious agents are not the only health concerns associated with wastewater and excreta. Heavy metals, toxic organic and inorganic substances also can pose serious threats to human health and the environment. Nitrates from the wastes can build up to high concentrations in groundwater and cause methaemoglobinaemia when consumed by bottle-fed infants. Nutrients may cause eutrophication in receiving water bodies potentially leading to cyanobacterial and other harmful algal blooms and the production of toxins by these organisms. Other chemicals such as pharmaceutical residues and potential endocrine disrupting substances have been identified in wastewater and excreta at low concentrations. Although the likelihood of health effects from exposure to these substances at these concentrations is assumed to be small, further research is needed to assess the actual health risks.

Estimates suggest that less than 5% of all sewage in developing countries receives any treatment before it is discharged into the environment (World Resources Institute, 1998). Industrialized countries also need to improve their sewage, excreta, and sludge management practices. For example, in the United States, the number of waterborne disease outbreaks and the number of affected individuals per outbreak has increased since 1940 (Hunter, 1997). Similarly, water quality monitoring of major European rivers indicates that average coliform levels have been steadily increasing for decades (Meybeck et al., 1990).

Despite more investment in water and sanitation projects in the last two decades, the total number of people without access to water and sanitation services remains stubbornly high, particularly in urban and peri-urban areas (WHO, 1997a). Worldwide efforts are required to reduce the transmission of waterborne diseases and decrease the flow of nutrients into areas prone to eutrophication and toxic algal blooms.

2. Economic Aspects of Health Effects

The failure to properly manage and dispose of wastewater and excreta has enormous financial implications. The costs of medical treatment and loss of productivity associated with diseases caused by exposure to contaminated food and water are most certainly high but have never been accurately estimated. Determining these costs is extremely difficult because there are so many different variables to consider. It is estimated that there are 4 billion cases of diarrhoea and 1.5 million acute cases of hepatitis A each year throughout the world (Murray & Lopez, 1996; WHO, 2000b) but assessing how many of these cases are directly connected to improper wastewater and excreta management/disposal is challenging. However, when different types of health interventions are evaluated it may be possible to provide a rough estimate of the percentage of these illnesses that can be attributed to improper waste and excreta management. For example, Esrey et al. (1991), found that sickness from diarrhoea was reduced by 25 - 33%, schistosomiasis was reduced by 77%, trachoma was reduced by 25%, and overall child mortality was reduced by 60% when well-designed basic water, sanitation and hygiene interventions were implemented at the community level. The World Bank (1993) estimated 40% reductions for both diarrhoea and intestinal worm infections using similar interventions.

In general, estimates of the costs that have been made for illnesses associated with improper waste management are country specific or are valid only for selected exposure pathways e.g., marine contamination-related diseases (Shuval, 2000). For example, in the US it has been estimated that waterborne diseases cost the country between 3 and 22 billion dollars per year in medical bills and lost productivity (Bennett et al., 1987; Murphy, 1999). In China illnesses related to water contaminated by untreated wastewater and excreta are thought to cost the country at least 3.9 billion dollars per year (World Bank, 1997). Shuval (2000) estimates that wastewater contamination of the marine environment is responsible for 250 million clinical cases of mild gastroenteritis and upper respiratory disease through recreational and other water contact, 2.5 million clinical cases of infectious hepatitis (Hepatitis A and E) acquired from consumption of contaminated seafood, and 100,000 - 200,000 cases of intoxication with algal biotoxins from consumption of contaminated seafood. Overall, these marine contamination-related diseases are thought to have an estimated economic impact of 13 billion dollars worldwide. WHO is also currently evaluating the estimated disease burden and associated costs of worldwide faecal-oral disease transmission related to improper wastewater and excreta disposal/management.

3. Health Effects Associated with Wastewater and Excreta

Wastewater and excreta consist of water (approximately 99%), micro-organisms (including human pathogens), and organic and inorganic substances including nutrients. The microbial pathogens (bacteria, helminths, protozoa, and viruses), heavy metals, nutrients, and organic compounds contained in wastewater and excreta pose a potential threat to human health and the environment. When improperly or untreated wastewater and excreta are released into the environment these substances can impact human health through the consumption of contaminated water, through the food chain, through poor personal hygiene, and through recreational or other contact with contaminated waters.

4. Pathogens

Pathogenic viruses, bacteria, protozoa and helminths (see table 1) are released from the bodies of infected persons in their excreta and may be passed on to others via either the mouth (e.g., through the drinking of contaminated water or eating contaminated vegetables/food) or the skin (as in the case of the hookworms and schistosomes). Excreta and wastewater generally contain high concentrations of excreted pathogens, especially in countries where diarrhoeal diseases and intestinal parasites are particularly prevalent.

Infectious diseases caused by pathogenic bacteria, viruses, protozoa or parasites are the most common and widespread health risks associated with drinking-water. Faecal contamination of drinking water is responsible for many disease outbreaks worldwide. The pathogens that most frequently cause disease include Salmonella spp., Shigella spp., pathogenic Escherichia coli, Vibrio cholerae, Yersinia enterocolitica, Campylobacter jejuni, hepatitis A viruses (and other viruses in table 1), Giardia spp., Cryptosporidium spp., and Entamoeba histolytica (WHO, 1993a). Most of these pathogens are distributed worldwide but outbreaks occur more frequently and endemicity is higher in areas where access to good quality water supplies and sanitation is limited.

In the 1990s, cholera reemerged as a major infectious disease as epidemics were reported in Africa, Asia, and South America. From 1991 to 1996 WHO estimated that there were between 70,000 and 160,000 cholera cases in Africa alone (WHO 1997b). The 1991 epidemic in Latin America caused 750,000 cases and 6500 deaths (PAHO, 1991). Cholera is primarily spread via faecally contaminated water and food. In 1970, a cholera epidemic in Jerusalem was traced back to the consumption of salad vegetables irrigated with raw wastewater. Health authorities isolated the same cholera strain from infected individuals, sewage, irrigated soil, and the irrigated produce. The epidemic quickly subsided after the authorities confiscated the vegetables grown with the untreated wastewater (Shuval et al., 1986). Cholera infections have also been linked to the consumption of contaminated seafood in the United States (CDC 1991; CDC 1996) and elsewhere. Although there is evidence that toxigenic strains of Vibrio cholerae have been spread from different regions by contaminated ballast, bilge water, and sewage dumped by ships from epidemic areas (McCarthy et al., 1992), it is unlikely that cholera will become endemic in areas with high standards of hygiene and sanitation.

Parasitic protozoa such as Cryptosporidium parvum and Giardia lamblia have recently been recognized as important causes of water and food-borne disease outbreaks associated with faecal contamination. These pathogens are particulary difficult to control because they are resistant to chlorine disinfection, persist in the environment, infect other animal hosts and may be difficult to diagnose and treat (WHO, 1993a). Cryptosporidium outbreaks have occurred worldwide due to contamination of drinking water, recreational waters and food. Serological studies of different populations indicate that prevalence of Cryptosporidium infection is very high. For example, in Anhui China, over half of the children by age five demonstrated antibodies to Cryptosporidium. In a poor area of Brazil, over 90% of the children developed antibodies to Cryptosporidium by the age of one. In some studies conducted in the United States, 17 - 32% of people exhibited serological evidence of Cryptosporidium infection by the time they became adults (Zu et al., 1994; Ungar et al., 1986; Ungar et al., 1988; Ungar et al., 1989).

Contamination of drinking water sources is also a problem in developed countries. In May 2000, an E. coli 0157:H7 outbreak occurred in Ontario Canada. In the outbreak more than 1000 people were infected and seven people died (Kondro, 2000). Similarly, in 1993, a cryptosporidium outbreak in Milwaukee, Wisconsin, U.S.A. affected approximately 400,000 consumers and caused 54 deaths - predominantly in immunocompromised persons (Kramer et al., 1996; Hoxie et al., 1997). Viruses, particularly Norwalk viruses and other human caliciviruses, were estimated to cause a large number of waterborne gastroenteritis outbreaks - as many as 6 million cases per year in the United States (Bennett et al., 1987).

Contact with faecally contaminated recreational waters has been associated with numerous disease outbreaks and unexpectedly high infection rates worldwide. Bathers and recreational water users frequently report gastro-intestinal symptoms, skin irritation, ear, nose, and throat infections, and respiratory infections (WHO, 1998). Gastro-intestinal symptoms have been directly correlated to concentrations of faecal bacteria found in fresh and marine waters (e.g., Escherichia coli, enterococci, and faecal streptococci) (PrEs, 1998). From 1997 to 1998, 32 disease outbreaks associated with recreational water were reported to the United States Centers for Disease Control. Of the gastroenteritis cases, half were caused by Cryptosporidium, 22% by bacteria and 11% by viruses (Barwick et al., 2000). Overall, Shuval (2000) estimates that, worldwide, there are 250 million clinical cases per year of mild gastroenteritis and upper respiratory disease due to bathing in contaminated waters.

Many types of pathogenic viruses have been identified in recreational waters. Griffin et al. (1999) found either enteroviruses, hepatitis A viruses, or norwalk viruses at 95% of 19 sampling sites in surface waters around the Florida Keys. Levy et al. (1998) found direct evidence of calicivirus outbreaks associated with recreational surface-water exposure.

Food that comes in contact with untreated or partially treated wastewater and excreta also can spread infectious diseases. Foods that are eaten raw or partially cooked are especially associated with the transmission of faecal-oral diseases. For example, some shellfish (such as mussels, oysters, and clams) obtain their food by filtering large quantities of water and are therefore particularly susceptible to contamination. Excreta-related human pathogens and heavy metals are taken in with the food particles and can be concentrated in the tissues. Shellfish are also frequently eaten raw or partially cooked. In 1988, the consumption of contaminated shellfish in Shanghai China led to an outbreak of Hepatitis A involving approximately 300 000 cases (Lees, 2000). Norwalk viruses have also been implicated in numerous disease outbreaks associated with the consumption of raw oysters (CDC, 2000).

Fish, and non-filter feeding shellfish (crabs, lobsters, prawns, shrimps) grown in faecally contaminated water containing high levels of human pathogens can concentrate the pathogens in their intestinal tracts and on their skin surfaces. When concentrations of faecally derived bacteria exceed a certain level they can be found in the muscle tissues of the fish. Infection may occur when the contaminated fish is consumed raw or lightly cooked. Cholera has been transmitted through contaminated fish and crabs in Guam and the United States respectively (CDC, 1996). Food handlers may also be at risk during preparation of the contaminated product.

Depuration, the transfer of fish or shellfish to non-contaminated water to cleanse the fish and shellfish of contamination prior to harvest, is widely practiced but, does not reliably remove bacteria or viruses from fish or shellfish muscle tissue.

The use of inadequately treated wastewater in irrigation is especially associated with elevated prevalence of intestinal helminth infection. For example, in Mexico, irrigation with untreated or partially treated wastewater was directly responsible for 80% of all Ascaris infections and 30% of diarrhoeal disease in farm workers and their families. However, when wastewater was retained longer in a series of retention ponds there was minimal risk of either Ascaris infection or diarrhoeal disease (Cifuentes et al., 2000). Ascaris infections in West Jerusalem were associated with the consumption of raw vegetables that were irrigated with untreated wastewater. When supplies of these vegetables were cut off, the number of Ascaris infections in the population dramatically decreased (Shuval et al., 1986).

Trematode infections are caused by parasitic flatworms (also known as flukes) that infect humans and animals. Infected individuals transmit trematode larvae in their faeces. Infections with trematode parasites can cause mild symptoms such as diarrhea and abdominal pain or more rarely, debilitating cerebral lesions, splenomegaly and death depending on the parasite load. In many areas of Asia where trematode infections are endemic, untreated or partially treated excreta and nightsoil are directly added to fish ponds. The trematodes complete their lifecycles in intermediate hosts and subsequently infect fish, shellfish, or encyst on aquatic plants. Humans become infected when they consume the fish, shellfish, or plants raw or partially cooked. WHO estimates that more than 40 million people throughout the world are infected with trematodes and that over 10% of the global population is at risk of trematode infection (WHO, 1995). Proper treatment of wastewater and excreta before it is introduced into fish ponds and thoroughly cooking fish, shellfish and plants are methods of breaking the lifecycle of these parasites.

Table 1: Pathogens Found in Untreated Municipal Wastewater and Excreta

Agent Disease
Campylobacter jejuni
Escherichia coli
E. coli
Helicobacter pylori
Legionella pneumophila
Salmonella (many serotypes)
Salmonella typhi
(several serotypes)
Vibrio cholerae
Yersinia enterocolitica
Gastroenteritis, long term sequelae (e.g. arthritis)
Bloody diarrhoea, hemolytic uremic syndrome
Abdominal pain, peptic ulcers, gastric cancer
Legionnaire's disease
Salmonellosis, long term sequelae (e.g. arthritis)
Typhoid fever
Shigellosis (dysentery), long term sequelae (e.g. arthritis)
Yersiniosis, long term sequelae (e.g. arthritis)
Ascaris (roundworm)
Ancylostoma (hookworm)
Clonorchis (liver fluke)
Fasciola (liver fluke)
Fasciolopsis (liver fluke)
Paragonimus (lung fluke)
Schistosoma (blood fluke)
Trichuris (whipworm)
Taenia (Tapeworm)
Schistosomiasis, Bilharzia
Balantidium coli
Cryptosporidium parvum
Cyclospora cayetanensis
Entamoeba histolytica
Giardia lamblia
Balantidiasis (dysentery)
Cryptosporidiosis, diarrhoea, fever
Persistent diarrhoea
Amebiasis (amebic dysentery)
Adenovirus (many types)
Astrovirus (many types)
Calicivirus (several types)
Enteroviruses (many types)
Coxsackie A
Coxsackie B
Norwalk virus
Hepatitis A virus
Hepatitis E virus
Parvovirus (several types)
Reovirus (several types)
Rotavirus (several types)
Respiratory disease, eye infections
Gastroenteritis, various
Herpangina, aseptic meningitis, respiratory illness
Fever; paralysis; respiratory, heart, and kidney disease
Fever, rash, respiratory and heart disease, aseptic meningitis
Paralysis, aseptic meningitis
Infectious hepatitis
Infectious hepatitis
Not clearly established
Source: National Research Council, 1998; Hurst et al., 1989; Sagik et al., 1978; and Edwards, 1992.


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