Waterborne illness and disease

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 in the twenty-first century, as around two billion people worldwide do not have access to safely managed drinking water at home, over one billion people lack basic drinking water service, and nearly 1.5 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 one million people worldwide, most of whom are children under age five, 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 ten people worldwide do not have access to potable water. Most 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 to 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 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 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, and Toxoplasma gondii. 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. According to the CDC, over 7 million Americans contract diseases spread through water each year, resulting in over $3 billion in healthcare costs.

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.

From 2015 to 2019, the CDC noted 208 reported outbreaks of waterborne disease associated with recreational water, resulting in 3,646 individual cases of illness, 286 hospitalizations, and thirteen deaths. Twenty-one of the outbreaks (23 percent of the total) were associated with untreated water, such as that in lakes or oceans, accounting for 479 of the individual cases. The primary bacteria involved were E. coli and Shigella sonnei. Avian schistosomes, a type of flatworm, accounted for most of the parasitic infections, and norovirus was the causative agent of the majority of 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 facilities, such as pools and water parks, accounted for sixty-nine of the outbreaks (77 percent) and approximately 1,309 individual cases of illness. The overwhelming majority of these cases—approximately 874 of them—were cryptosporidiosis, since Cryptosporidium has a very high tolerance for chlorine. Only seventy-five cases were caused by bacterial pathogens and 122 by viral pathogens. The most common bacterium responsible for infection was Legionella, and norovirus was the causative agent for all 122 viral cases. 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 drinking water purity. In developing countries, thermal or ultraviolet disinfection is a potential option because of its relatively low cost and lack of chemical additives. In extremely impoverished areas where electricity is unavailable at the household level for boiling water or ultraviolet disinfection, WHO proposes that disinfection can be performed using solar heating. Other less common water purification methods include the 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 drinking water contamination 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 non-threatening to human health are also of concern to 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. For example, temperature increases may provide a more hospitable environment for pathogens, fostering better growth, survival, and infectivity of waterborne illnesses. 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 Campylobacterota 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. The bacteria Vibrio cholerae causes between 1.3 and 4 million cases of cholera each year, leading to between 21,000 to 143,000 deaths. 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. In the 2020s, outbreaks of cholera continued to be problematic, mostly in countries in southern Africa.

Schistosomiasis infects millions of people worldwide, causing up to 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. At the forefront is the United Nations, which addresses water quality in the sixth of its Sustainable Development Goals. One component of this goal is to ensure universal and equitable access to clean water for all by 2030, along with equitable sanitation. Achieving this goal has the potential to save 829,000 lives annually from diseases linked to unsafe sanitation and drinking water.

Demands for clean water are exceeding the supply of potential fresh-water sources, as the world’s population continues to increase. The World Economic Forum listed the global water crisis as the fifth global risk to society in 2021. 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.

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