Waterborne diseases are generally spread by contamination of drinking water systems by the urine and faeces of infected animals or people.
This is likely to occur in places where public and private drinking water systems get their water from surface waters (rain, creeks, rivers, lakes, etc.), which can be contaminated by infected animals or people. Runoff from landfills, septic fields, and sewer pipes, residential or industrial developments can also contaminate surface water.
This contamination has been the cause of many dramatic outbreaks of faecal-oral diseases such as cholera and typhoid. However, there are many other ways in which faecal material can reach the mouth, for instance through the hands or on contaminated food. In general, contaminated food is the single most common path in which people become infected.
The germs in the faeces can cause a disease by even slight contact and transfer. This contamination may occur due to floodwaters, water runoff from landfills, septic fields, and sewer pipes. The following picture shows the faecal-oral routes of diseases transmission (Fig. 2.1).
Figure 2.1: Faecal-oral route of disease transmission
The only way to break the continued transmission is to improve people’s hygienic behavior and to meet their basic needs of: drinking water, washing and bathing facilities and sanitation. For example, malaria transmission is facilitated when large numbers of people sleep outdoors during hot weather, or sleep in houses that have no protection against invading mosquitoes. Malaria mosquitoes, tropical black flies, and bilharzias snails can all be controlled with efficient drainage because they all depend on water to complete their life cycles.
Clean water is a prerequisite for reducing the spread of waterborne diseases. It is well recognized that the prevalence of waterborne diseases can be greatly reduced by provision of clean drinking water and favorable conditions for safe disposal of faeces.
Water is disinfected to kill any pathogens that may be present in the water supply and to prevent them from growing again in the distribution system. Disinfection is then used to prevent the growth of pathogenic organisms and to protect public health; the choice of the disinfectant depends upon the water quality and water supply system. Without disinfection, the risk of waterborne diseases is increased. The two most common methods to kill microorganisms in the water supply are: (i) oxidation with chemicals such as chlorine, chlorine dioxide or ozone, and (ii) irradiation by ultraviolet (UV) radiation (URL8).
The health risk related to the presence of toxic chemicals in drinking water differs from the risk caused by microbiological contaminants. There are few chemical constituents in the water that can lead to acute health problems apart from the chance of massive accidental contamination of a water supply. Moreover, experience shows that, in such incidents, the water usually becomes undrinkable due to unacceptable taste, odor, and appearance.
New compounds continually enter the environment, either through intended use (such as in pesticides and fumigants), or via industrial, human, or animal waste (such as detergents, pharmaceuticals, antibiotics, and synthetic hormones). Because chemical contaminants are not normally associated with acute effects, they are, unfortunately, placed at lower priority than microbial contaminants, whose effects are usually acute and widespread.
The problems associated with the chemical constituents of drinking water arise primarily from their ability to cause adverse health effects after prolonged periods of exposure; of particular concern are contaminants that have cumulative toxic properties, and substances that are carcinogenic.
Among compounds found in water that accumulate in the environment and in the human body, the principal ones are:
However, it is unlikely that all these contaminants occur in all water supplies or even in all countries. For the chemical contaminants, in particular, some factors should be considered, including the geology of the region and the types of human activities that take place (agriculture, industries, etc.).
Pollution of water by metals or persistent organic pollutants (POP) may directly or indirectly, through air and soil, contaminate food.
It should be noted that the use of chemical disinfectants for water treatment usually results in the formation of chemical by-products, some of which are potentially hazardous. However, health risks owing to these by-products are extremely small in comparison with the risks associated with inadequate disinfection, and it is important that disinfection should not be compromised in attempting to control the by-products.
The radiological health risk associated with the presence of naturally occurring radionuclides in drinking water should also be taken into consideration, although the contribution of drinking water to total ambient exposure to these radionuclides is very small under normal circumstances. The guideline values generally recommended do not apply to water supplies contaminated during emergencies arising from accidental release of radioactive substances to the environment.
Over the past century, deaths from infectious diseases borne by water (cholera, typhoid, diphtheria) declined significantly in Europe. However, water pathogens remain a significant cause of illness. In the last 20 years, new germs have emerged as additional threats while diseases once thought to be under control, have become increasingly prevalent. Infections can be rapidly and widely disseminated through water and are particularly threatening to communities that have little or no resistance to them (URL9). Those at greatest risk of waterborne disease are infants and young children, people who are debilitated or living in unsanitary conditions, the sick, and the elderly. For these most vulnerable people, the infectious doses are significantly lower than for the general adult population. The potential consequences of microbial contamination are such that its control must always be a priority.
The assessment of the risks associated with variation in microbial quality of the water is difficult and controversial because of insufficient epidemiological evidence, the number of factors involved, and the changing interrelationships between these factors. Тhe greatest microbial risks, however, are generally associated with ingestion of water contaminated with human/animal excreta. There are indicator parameters that corroborate the presence of faecal contamination (total coliforms, faecal coliforms, faecal streptococci), but their absence does not prove the absence of contamination.
Microbial risk can never be entirely eliminated because waterborne diseases may also be transmitted through person-to-person contact, aerosols, and food intake; thus, a reservoir of cases and carriers is maintained. Provision of safe water supply in these circumstances will reduce the chances of spread by the other routes. Waterborne outbreaks are particularly to be avoided because of their capacity to result in the simultaneous infection of a high proportion of the community.
Aquatic environment systems and surface waters contain a great variety of micro-organisms (bacteria, viruses, yeasts, parasites, helminths, etc.), some of which are able to adopt a form that could resist living conditions that would otherwise be unsuitable. Some of these organisms are causative agents (pathogens) of human communicable diseases or such that find the right environment in water for the breeding and propagation of their vectors. For instance, irrigation and drainage project developments create great expanses of water and, provided there are a number of favorable ecological conditions, may lead to the introduction of disease vectors in areas where they have not occurred before, or to a rapid increase in their original density. Wherever a parasite or another disease causing organism is present, and a susceptible human population exists, environmental changes resulting from such projects may have a profound impact on the epidemiology of diseases through their effect on vector bionomics.
Typical waterborne microbial diseases and their importance worldwide are summarized in Tables 2.1 and 2.2.
This classification relates to the following conditions responsible for the persistent high prevalence of these diseases:
Table 2.1. The most common pathogenic microorganisms causing waterborne diseases
|Adenovirus Infection||Adenoviridae virus||Varying depending on which part of the body is infected||Drinking contaminated water||5-8 days|
|Amebiasis||Entamoeba histolytica parasite||Diarrhea, stomach pain, stomach cramps||Fecal matter of an infected person (usually ingested from a pool or infected water supply)||2 to 4 weeks|
|Campylobacteriosis||Campylobacter jejuni bacteria||-||Chicken, unpasteurized milk, water||2 to 10 days|
|Cryptosporidiosis||Cryptosporidium parasite||Stomach cramps, dehydration, nausea, vomiting, fever, weight loss||Fecal matter of an infected person (can survive for days in chlorinated pools)||2 to 10 days|
|Cholera||Vibrio cholerae bacteria||Watery diarrhea, vomiting, leg cramps||Contaminated drinking water, rivers and coastal waters||Two hours to 5 days|
|E. Coli 0157:H7||Escherichia coli bacteria||Diarrhea (may be bloody), abdominal pain, nausea, vomiting, fever, HUS||Undercooked ground beef, imported cheeses, unpasteurized milk or juice, cider, alfalfa sprouts||1 to 8 days|
|Giardiasis||Giardia lamblia parasite||Diarrhea, excess gas, stomach or abdominal cramps, upset stomach or nausea||Swallowing recreational water contaminated with Giardia||1 to 2 weeks|
|Hepatitis A||Hepatitis A virus||Fever, fatigue, stomach pain, nausea, dark urine, jaundice||Ready-to-eat foods, fruit and juice, milk products, shellfish, salads, vegetables, sandwiches, water||28 days|
|Legionellosis||Legionella pneumophila bacteria||Fever, chills, pneumonia, anorexia, muscle aches, diarrhea, vomiting||Contaminated water||2-10 days|
|Salmonellosis||Salmonella bacteria||Abdominal pain, headache, fever, nausea, diarrhea, chills, cramps||Poultry, eggs, meat, meat products, milk, smoked fish, protein foods, juice||1-3 days|
|Vibrio Infection||Vibrio parahaemolyticus, Vibrio vulnificus bacteria||Nausea, vomiting, headache (a quarter of patients experience dysentery-like symptoms)||Raw shellfish, oysters||1 to 7+ days|
Table 2.2. Some water-related diseases and their importance worldwide
|Disease group||Disease||Estimated infection rate|
|Waterborne diseases||Diarrhoeal diseases||not available||1,000,0001)||5,0001)|
|Waterborne diseases||Diarrhoeal diseases||not available||1,000,0001)||5,0001)|
|Water-washed diseases||Ascariasis (=roundworm infection)||800,000-1,000,000||1,000||20|
|Ancylostomiasis (=hookworm infection)||700,000-900,000||1,500||50-60|
|Water-based diseases||Schistosomiasis (Bilharzia)||200,000||?||500-1,000|
|Water-related vector-borne diseases||Malaria||240,000||100,000||not available|
|Japanese encephalitis||not available||20-40||case fatality ratio between 10-30 %|
Water-related diseases can be classified into 4 major categories (Table 2.3).
Table 3. Classification of water-related diseases (adapted from the WHO’s definitions)
Diseases spread through faecal or chemical contamination of drinking water (cholera, typhoid fever, hepatitis A, bacterial dysentery, amoebic dysentery, amoebic meningo-encephalitis, crytosporidiosis, giardiasis, methaemoglobinaemia, dental and skeletal fluorosis). Widely distributed in Europe.
Prevention: the pathogen is usually carried in the contaminated drinking water and is directly transmitted through it. Nonetheless, dirty hands or food are at least as often to blame. Washing with water free of contamination (and proper drying) is very important.
Diseases due to the lack of water for proper sanitation and hygiene (e.g., trachoma, skin infections, ascariasis = roundworm infection; ancylostomiasis = hookworm). The prevalence of these infections varies with climate conditions; however, they are present in all parts of Europe. Domestic dogs and cats (puppies, kittens, and pregnant and nursing animals), with high rates of ascarid and hookworm infections, and pica (eating of substances with no nutritional value, such as dirt or paint) are the principal risk factors for human disease in Europe.
Prevention: hand washing and good personal hygiene, eliminating intestinal parasites from pets through regular deworming, and making potentially contaminated environments (e.g., unprotected sand boxes) off limits to children.
Parasitic infections transmitted through an intermediate host (an invertebrate organism), as the pathogen requires an aquatic or semi-aquatic environment for a part of its life cycle. Infection can occur by drinking (dracunculiasis = guinea worm infection), by direct contact with the infested water (schistosomiasis = snail fever), or by eating insufficiently cooked snails. Usually not found in Europe.
Prevention: avoid wading in the water or imbibing it; clear the snails or fleas from the water source; filter/boil drinking water; drink only water from underground sources that are free from contamination; prevent persons with an open worm ulcer from entering ponds and wells with drinking water; cook snails properly before eating.
|4. Water-related or vector-borne diseases||
Diseases transmitted by insects that depend on water for their propagation (insects that bite or breed near water; insects having aquatic immature stages (e.g., onchocerciasis, sleeping sickness, filiariosis, malaria, dengue, yellow fever). Except for some isolated cases, not extended to Europe.
Prevention: The vectors – flies and mosquitoes – have to be controlled by spraying and drainage; or the parasites they carry have to be eradicated by eliminating the disease in humans. Environmental health engineering management combined with chemical and biological control measures whenever appropriate.
Recreational water illnesses (RWI) refer to a spectrum of illnesses acquired through swallowing, breathing or coming into contact with contaminated water in recreational water locations, which include treated or disinfected venues such as swimming pools, water parks, and hot tubs, but also untreated or naturally occurring bodies of water, such as lakes, rivers, and the sea (URL8 and URL9). Emerging zoonoses that may be transmitted by faeces through the waterborne route have not been all well defined. However, a variety of infections (e.g., skin, ear, eye, respiratory, neurologic, and diarrheal infections) have been linked to wading or swimming in water, particularly if the swimmer's head is submerged. Water may be contaminated by other people and from sewage, animal wastes, and wastewater runoff. Some bodies of water may be contaminated by urine from animals infected with organisms like Leptospira. The spectrum of RWIs includes ear, eye, gastrointestinal, neurologic, and respiratory and skin infections. Diarrheal illnesses are the most reported RWIs. Waterborne diarrheal pathogens include viruses (noroviruses), bacteria (E. coli, Shigella), and parasites (Cryptosporidium, Giardia). People most susceptible to gastrointestinal RWIs are the young, the elderly, the pregnant and the immuno-compromised.
People who want to swim in nature should be advised to avoid beaches that may be contaminated by human sewage or dog feces. Therefore, it is recommended for people to avoid submerging their heads and to wear nose plugs when entering untreated water to prevent water getting up the nose.
Accidental swallowing of small amounts of fecal contaminated water can be sufficient to infect. Swimmers should be warned to try to avoid swallowing water while undertaking aquatic activities. Generally, pools that contain chlorinated water can be considered safe places to swim if the disinfectant levels and pH are properly maintained. However, some organisms (e.g., Cryptosporidium, Giardia, Hepatitis A virus, and Norovirus) have moderate to very high resistance to chlorine levels commonly found in chlorinated swimming pools, thus swallowing of chlorinated swimming pool water may also pose a risk of contracting the disease. People who have diarrhea should refrain from swimming to avoid contaminating recreational water.
When someone has open cuts or abrasions that might serve as entry points for pathogens, they should be advised to avoid swimming or wading. In certain areas, fatal primary amoebic meningo-encephalitis has occurred after swimming in warm freshwater lakes or rivers, thermally polluted areas around industrial complexes, and hot springs.
RWI transmission occurs in recreational water that is non-chlorinated or inadequately chlorinated, but may also occur in adequately maintained venues when chlorine-resistant pathogens are involved. Because of the complex nature of RWI transmission, it is essential to incorporate a multidisciplinary approach in prevention and control strategies.
Human behavior plays a crucial role in RWI transmission. Swimmers who are symptomatic with diarrhea, as well as toddlers and diaper-aged children may contaminate the water in which there are healthy co-swimmers.
In addition, high-risk groups such as the young, the elderly, the pregnant and the immuno-suppressed, should also be advised about healthy swimming habits. Healthcare providers may help to teach parents of sick children and patients about healthy swimming habits. These simple and practical messages include the following:
It is also judicious to recommend for patients with infectious diarrhea to refrain from swimming for two weeks after cessation of diarrhea, particularly if they are infected with Cryptosporidium or Giardia, as these may still be excreted for several weeks after symptom resolution.
If a medical emergency in relation to water occurs, it is important to contact the physician and the local public health authorities/the regional epidemiologist.
In times of extreme crisis, local health authorities may urge consumers to be more cautious or to follow additional measures. When home water supply is interrupted by natural or other forms of disaster, limited amounts of water can be obtained by draining the hot water tank or by melting ice cubes. In most cases, water from wells is the preferred source of drinking water. If it is not available and river or lake water must be used, sources containing floating material should be avoided as well as water with a dark color or an odor.
Diarrhea and other serious waterborne infections can be spread when disease-causing organisms from either human or animal faeces are introduced into the water. However, even with the modern technology, specific detection of animal faeces in water is still not possible, because traditional bacterial indicators of faecal contamination cannot distinguish human faeces from animal faeces. Because of this inability to distinguish human from animal faecal contamination, resource managers and regulators have opted to treat all faecal contamination as equally hazardous to human health. This approach frequently results in the closure of beaches and shellfish harvesting areas that are affected by storm water runoff that carries faecal indicator bacteria. The risks related to exposure to these waters contaminated by animals is unknown. Studies that have attempted to define the risks associated with swimming in animal-contaminated water have not given a clear indication that there is an excess illness rate related to this type of exposure. These equivocal results do not lead to the conclusion that all faecal contaminated waters should be treated alike. We need to study the risks posed by animal faecal wastes to users of water resources and to find proper indicator systems that identify animal contamination of surface waters. The availability of more research data that would meet the latter two information needs would significantly improve our ability to manage water resources.
In northern, western and southern Europe, the drinking water supply is normally safe and regularly controlled. But if a break of the water main, a leak in waste water collecting pipe, an interruption or a problem at the water treatment plant occurs, a serious drinking water contamination problem will result and has to be faced promptly. Here again, when an emergency in relation to water occurs, it is important to rapidly contact a physician and the local public health authorities/the regional epidemiologist.
Establish key contacts at partner institutions such as local public health authorities, laboratories, the media, daycare centers, etc.
Check resources and contingency plans. Start elaborating a plan of what types of equipment and other resources may be needed. Some resources might come from the public health authorities.
Share information with other regional/provincial/departmental/national public health authorities and facilities. This can speed up the investigation process and help health departments fill knowledge gaps.
At the beginning of an outbreak, it is very important to identify as many confirmed cases as possible to help find the source of the outbreak. This can be done through mass mailings, newspaper ads, etc.
If possible, establish a hotline for outbreak-related calls.
Before beginning the examinations, get a realistic idea of the turnaround time on laboratory tests.
Consider using private labs/hospitals, as well as government facilities.
Make periodic, regularly scheduled conference calls with established key contacts. Keep everyone informed, plan next steps, share information, etc.
Decide what information is to be shared and how to share it.
Decide on a mechanism to use in sharing information, such as e-mail or fax. Make sure all channels of communication are in working order.
Keep repertories of phone calls regarding the outbreak.
Document the number of man-hours spent on the outbreak for future budgetary/resource reference.
Establish contact points with media sources.
If necessary, form a working group to establish good relationships with the media.
Give them fact sheets on the pathogen.
Send out frequent updates to keep the media correctly informed.
When putting together a press release on the pathogen, include any information from existing pathogen-specific fact sheets.