What are waterborne illnesses and diseases?

Definition

Waterborne illnesses and diseases are transmitted primarily through the ingestion of
water that is contaminated (infested) by microorganisms or toxins. Contact with infested water
that allows pathogens to enter through broken skin is another method of
disease transmission.

There are four primary types of waterborne illness: waterborne disease, which is contracted by ingesting contaminated drinking water; water-washed disease, which is spread through an improper or inadequate sewage system; water-based disease, which is transmitted by an organism that lives in the water, such as a worm or fish; and water-related vector-borne disease, which is transmitted by vectors (such as mosquitoes) that breed in water.

Global Reach

Waterborne illness is a major global health problem, as nearly 900 million people worldwide do not have access to potable (drinkable) water and 2.5 billion people live without basic sanitation. Diarrheal diseases contracted as a result of inadequate sanitation are the leading cause of illness and death globally. Approximately 2 million people worldwide, most of whom are children less than five years of age, die each year from waterborne diarrheal illnesses.

Waterborne illnesses are common in developing areas in the world, where poverty, political conflict, and other factors prevent the construction of infrastructures that provide adequate sanitation and sewage treatment facilities. Sporadic outbreaks of waterborne diseases still occur, however, in countries with well-established water-purification and sewage systems.

Water may be contaminated either at the source or at post-purification as it
travels through the drinking water supply system (DWSS). Although waterborne
illnesses are commonly associated with drinking water and sanitation, other
points of human contact with water also can cause infection and disease. Humans
can become infected through water-based recreation, bathing, food production, and
irrigation.

Unsafe Drinking Water

Although considered a basic human right by the United Nations, one in six
people worldwide do not have access to potable water. Most of the diseases
transmitted through drinking water are spread through fecal-oral
transmission and are therefore directly linked to poor
sanitation. The major microorganisms causing waterborne diseases through
contaminated drinking water are bacteria, viruses, and protozoa.
More than 1,415 species of pathogenic microorganisms have been identified as
causing waterborne disease; however, in countries with adequate sanitation systems
and clean drinking water, most of these diseases are not of special concern for
public health officials.

The major bacterial contaminants of drinking water that cause illness in humans
are Escherichia coli
, Enterococcus faecalis
, Salmonella
species (spp.), Shigella
spp., Aeromonas
spp., Vibrio cholerae
, Yersinia enterocolitica
, Campylobacter
spp., Legionella pneumophila
, Leptospira
spp., and various mycobacteria. Most of these organisms cause gastroenteritis and diarrhea, although several
Salmonella strains and Leptospira spp. cause
infectious fevers; L. pneumophila and mycobacteria cause
respiratory infections. All of these organisms are excreted in human feces, with
the exception of L. pneumophila, Leptospira
spp., and mycobacteria.

Major viral human pathogens in drinking water include enterovirus (polio, coxsackie, and echo), rotavirus, adenovirus, hepatitis A
and E, and norovirus. All of these pathogens have the potential to cause fatal diseases,
with rotavirus being one of the most dangerous gastrointestinal viruses for
children. All are transmitted by human feces except the norovirus, which is
carried through water and can be deposited on and retrieved from inanimate objects
(fomites). The enteroviruses cause meningitis, polio, and
encephalitis. Adenoviruses and rotaviruses cause
gastroenteritis, while the hepatitis viruses cause infectious hepatitis
(hepatitis
A) and liver damage. Viruses are difficult to detect in
drinking water because they are not identifiable by traditional cell-culture
techniques.

The pathogenic protozoa of concern for drinking water are
Cryptosporidium parvum
, Cyclospora cayetanensis
, Entamoeba histolytica
, Giardia intestinalis
(also known as G. lamblia), and Toxoplasma
gondii
. All of these pathogens cause diarrhea or dysentery in humans, except T. gondii. Most pathogenic
protozoa are transmitted through human or animal feces into water in the cystic
phase of the life cycle, making them highly resistant to chlorination.
Furthermore, bacteria may live within protozoa, protecting the bacteria from
chlorination.

In the United States and other developed countries, most water contamination occurs after the purification process. That is, contamination occurs in the water system, at the distribution point (tap or fountain), during the transfer and processing of water to be bottled, or during storage. In 2005-2006, a reported 612 cases of waterborne illness in the United States were caused by water for drinking, resulting in four deaths. More than one-half of the waterborne illnesses were caused by organisms introduced after disinfection, and the majority of these cases were caused by Legionella.

Bacterial
infections were contracted by a reported 135 people. Most of
the illnesses were caused by Legionella spp., 32 were caused by
Campylobacter spp., and the remainder were caused by other
pathogens. All four deaths were caused by Legionella, which
regrows in warm-water systems, and all occurred in hospitals or long-term care
facilities. Viral pathogens were the causative agents of 212 cases of illness, 196
from norovirus and 16 from hepatitis A. These outbreaks were associated with
untreated well or spring water at private residences. G.
intestinalis and Cryptosporidium spp. were associated
with 41 and 10 cases of illness, respectively.

Water-Based Diseases

Water-based diseases are transmitted by an organism that lives in the water,
such as a worm or a fish, and are contracted by contacting or ingesting the water.
The most recognized examples of water-based diseases are schistosomiasis and ascariasis.
Both of these infections are common in developing countries and are caused by
trematodes and helminths, respectively. Humans usually contract these diseases
when bathing or playing in contaminated water, where larvae or eggs enter the body
through broken skin. As the parasites reproduce, they cause severe abdominal and
intestinal symptoms that can be fatal.

Waterborne illnesses can also be transmitted through bodies of water used for recreational activities, such as lakes, reservoirs, pools, and water parks. Recreational lakes and reservoirs can contain fecal contaminants from humans and animals, especially E. coli, Shigella spp., Salmonella spp., enterococci, norovirus, Cryptosporidium spp., and G. intestinalis. Contaminants enter the water from improperly treated or leaking wastewater from residential areas and farms, from already-infected swimmers, and from wildlife. In 2005 and 2006 in the United States, there were 245 cases (6 percent of total cases) of waterborne diseases contracted at untreated water facilities. The primary bacteria involved were Leptospira spp. and Shigella sonnei. Cryptosporidium spp. accounted for most of the protozoan infections, and norovirus was the causative agent of all of the viral infections. Because of the types of activities involved, these illnesses result in not only intestinal infections but also skin, eye, ear, nose, throat, and respiratory infections.

Waterborne illnesses at treated water parks accounted for 94 percent of all
cases reported in 2005 and 2006 in the United States. The overwhelming majority of
these cases (87 percent) was caused by protozoa, as protozoa are difficult to kill
with chlorination; 98 percent of all protozoan infections were cryptosporidiosis. Only 6 percent of cases was caused by
bacterial pathogens and 2 percent by viral pathogens. The bacterial pathogens were
transmitted either in swimming pools, in which a number of toddlers wearing
diapers were present, or in warm-water spas for adults.
Cryptosporidium spp. transmission occurred in several splash
parks and water parks across the United States that did not have ozone or
ultraviolet light disinfection units (which can kill cysts) as a backup to
chlorination. In these and other outbreaks, the cryptosporidiosis could be
attributed to already-infected visitors to the park contaminating the water
supply. Cryptosporidiosis is highly infectious and can be transmitted with the
ingestion of as few as ten cysts.

Water-Related Vector-Borne Diseases

Water-related vector-borne diseases are transmitted by insect vectors that
breed in stagnant pools of water. These diseases include malaria and
West Nile
virus infection, both of which are transmitted by mosquitoes
that lay eggs in stagnant water.

Prevention

Chlorination (chlorine, chloramines, chlorine dioxide) is used to disinfect drinking water. This method is usually sufficient, provided the source water is reasonably clear. Along with chlorination is filtration, which removes particulate matter, and microfiltration, which removes protozoa in the cyst phase. Many water-treatment facilities use a combination of purification methods to ensure that all types of microorganisms have been eliminated.

According to the World Health Organization (WHO), ozone is the most effective disinfection method because it can eliminate
Cryptosporidium species. WHO recommends a combination of ozone
and chlorine for maximum purity of drinking water. In developing countries,
thermal or ultraviolet disinfection is a potential option because of its
relatively low cost and because of the lack of chemical additives. In poor areas
where power is unavailable at the household level for boiling water or for
ultraviolet disinfection, WHO proposes that disinfection can be performed using
solar heating. Other less common methods of water purification include
precipitation of impurities with coagulation agents, adsorption of impurities onto
organic materials, ion-exchange treatment, and treatment with acids or bases.

A main source of contamination of drinking water after purification is sewage
influx from industrial and residential areas; cities pose the greatest risks.
Other sources of post-purification contamination include flood waters, which
introduce sewage overflow; microorganisms resistant to disinfectant procedures;
increased virulence of pathogens; and emerging new pathogens. Drinking
water can also be recontaminated through biofilms. As water flows through the DWSS, solid materials settle onto pipes,
providing a surface onto which microorganisms can adhere and grow; this adherence
leads to the formation of biofilms. Biofilms comprise a small ecosystem of various
types of interacting microorganisms. Because of their complexity, biofilms present
a challenge to keeping water clean in the DWSS.

Pathogens that were previously nonthreatening to human health also present concern for public health officials. Changes in the climate or environment may alter the microbial composition of the source water, requiring a change in the purification process. Previously controlled pathogens may develop resistance to disinfection procedures or may become more virulent, meaning that a smaller number of organisms are required to cause disease. Emerging pathogens (such as Epsilonproteobacteria and Helicobacter pylori) that have not been considered a threat to the drinking water supply are now being monitored. All of these circumstances require changes to the purification and monitoring protocols.

In the United States, public drinking water quality is regulated by the
Environmental
Protection Agency (EPA). Limitations have been established for more than ninety
microbiological and other contaminants. For the disease-causing microorganisms
Cryptosporidium spp., G. intestinalis,
L. pneumophila, and viruses, the requirement is 99.9 percent
removal/inactivation. Other nonpathogenic bacteria commonly found in source water
are also tested to evaluate the maintenance of the water system (no requirement).
Tests for coliforms including E. coli are performed as indicators
of the presence of other pathogens (limit 5 percent).

Recreational water facilities in the United States are variously regulated. For treated water facilities, including water parks and swimming pools, state and local agencies are responsible for the development and oversight of any health codes. Untreated recreational areas are regulated by EPA guidelines. For fresh-water recreational areas, the EPA limits are 33 colony-forming units (CFU) per 100 milliliters (mL) for enterococci and 126 CFU per 100 mL for E. coli. For ocean beaches, the guideline is 33 CFU per 100 mL for enterococci, with each locality having final authority over closure of swimming areas.

Impact

The impact of waterborne diseases worldwide is staggering, as they currently
account for 4 percent of the global disease burden. Approximately two million
people worldwide die each year from waterborne diarrheal illnesses, 75 percent of
whom are children. Cholera is still present in more than
fifty countries, causing 3 to 5 million cases and 100,000 deaths annually. From
2004 to 2008, the number of cholera cases increased 24 percent, indicating an
increase in the number of people living in crowded, unsanitary conditions.

Schistosomiasis infects 207 million people worldwide, causing about 200,000 deaths per year, mainly in sub-Saharan Africa. Ascariasis infects up to 10 percent of people in developing countries, leading to approximately 60,000 deaths per year. Both diseases target children who frequently play in infested waters.

Water quality has been the focus of the health improvement programs of several global health organizations. In the forefront is the United Nations, which addresses water quality in the seventh of its 2015 Millennium Development Goals. One component of this goal is to cut by one-half by 2015 “the proportion of the [world’s] population [that lives] without sustainable access to safe drinking water and basic sanitation.” The U.N. is on track to meet this goal, having provided 86 percent of the world’s population access to safe drinking water. However, the goal to provide basic sanitation will likely not be met.

Demands for clean water are exceeding the supply of potential fresh-water sources, as the world’s population continues to increase. The increased diversion of water supplies for agriculture has resulted in less water for human consumption and in higher contamination of drinking water with farm wastewater. Experts also predict that climate change will adversely affect drinking water sources globally.

Bibliography

Ashbolt, Nicholas J. “Microbial Contamination of Drinking Water and Disease Outcomes in Developing Regions.” Toxicology 198 (2004): 229-238. Summary of the most common pathogens causing waterborne diseases and of the extent of these diseases in developing nations.

Brettar, Ingrid, and Manfred G. Hofle. “Molecular Assessment of Bacterial Pathogens: A Contribution to Drinking Water Safety.” Current Opinion in Biotechnology 19 (2008): 274-280. A summary of detection methods for bacterial pathogens in drinking water.

Bridge, Jonathan W., et al. “Engaging with the Water Sector for Public Health Benefits: Waterborne Pathogens and Diseases in Developed Countries.” Bulletin of the World Health Organization 88 (2010): 873-875. A brief overview of waterborne illnesses as a public health issue and of recent outbreaks in developed countries.

Percival, Steven L., et al. Microbiology of Waterborne Diseases. San Diego, Calif.: Academic Press/Elsevier, 2004. Major pathogenic waterborne microorganisms are described in terms of physiology, reproduction, clinical features and treatment of infection, and survival in the environment.

Snelling, William J., et al. “Bacterial-Protozoa Interactions and Update on the Role These Phenomena Play Towards Human Illness.” Microbes and Infections 8 (2006): 578-587. Discusses the bacterial-protozoan interactions in water systems that hinder the detection and eradication of pathogenic organisms in drinking water.

Soller, Jeffrey A., et al. “Estimated Human Health Risks from Exposure to Recreational Waters Impacted by Human and Non-human Sources of Faecal Contamination.” Water Research 44 (2010): 4674-4691. This study compared the risks associated with human, gull, chicken, pig, and cattle fecal contamination of recreational swimming areas.

Woodall, C. J. “Waterborne Diseases: What Are the Primary Killers?” Desalination 248 (2009): 616-621. A brief review of frequently reported causative agents of waterborne diseases.