Which waterborne illnesses are most common?

In 2020, a Centers for Disease Control and Prevention (CDC) study estimated that waterborne illnesses affect around around 7.2 million Americans annually. These illnesses can spread through drinking water, recreational bodies of water like swimming pools and lakes, and via water used for agriculture.

What is a waterborne illness?

Waterborne illnesses are diseases caused by pathogens — bacteria, viruses, and parasites — that travel via water and are contracted by drinking or encountering contaminated water.

What are the most common waterborne illnesses?

Per CDC estimates, the five most common waterborne illnesses in the US are:

• Otitis externa or "swimmer’s ear": A bacterial infection that typically occurs when water stays in the outer ear canal for too long. Although more prevalent among children, anyone can get swimmer’s ear. It’s not contagious.
• Norovirus: A highly contagious virus that spreads through contaminated food or water — it’s considered both a foodborne and waterborne illness. It often spreads when an infected person handles food without washing their hands first.
• Giardiasis: A waterborne illness triggered by the microscopic parasite Giardia duodenalis. Giardia parasites spreads by being ingested in contaminated water or food. After infection, the parasite lives in the intestines and can be passed through fecal matter.
• Cryptosporidiosis: Cryptosporidium, often called “Crypto,” is a microscopic parasite that causes the diarrheal disease cryptosporidiosis. The primary symptom of a Cryptosporidium infection is watery diarrhea. Other symptoms include stomach cramps or pain, dehydration, nausea, vomiting, fever, and weight loss. It can be spread through drinking contaminated water or coming in contact with contaminated fecal matter.
• Campylobacteriosis: An illness caused by the bacteria Campylobacter, and the most common bacterial cause of diarrheal illness in the United States. Campylobacter spreads mainly through consumption of raw or undercooked poultry, or foods that have been in contact with raw poultry. It can also be transmitted through other foods, contact with infected animals, and untreated water.

Otitis externa, also known as swimmer’s ear, affects up to 7.3 million people (nearly the population of Arizona) every year, and Norovirus affects up to 5.5 million people (a bit fewer than live in Minnesota).

How many people die from waterborne illnesses every year?

The CDC estimates that 6,630 people die annually from waterborne illnesses. The waterborne illness estimated to cause the highest number of deaths is nontuberculous mycobacterial (NTM) infection, followed by Legionnaires’ disease, pseudomonas (pneumonia and septicemia), and otitis externa or swimmer’s ear.^[1]

• Nontuberculous Mycobacteria (NTM) Infections: Mycobacterial organisms found in the environment spread infections through exposure to soil, dust, and water — lakes, streams, rivers, and municipal water sources.
• Legionnaires’ disease: A severe and potentially life-threatening form of pneumonia caused by the Legionella bacteria, which can be found in natural freshwater sources and can also grow in human-made water systems.
• Pseudomonas pneumonia and septicemia: Pseudomonas aeruginosa bacteria can be found in pipes and faucets, as well as in medical equipment such as ventilators and catheters. The pseudomonas aeruginosa bacteria can cause pneumonia, septicemia, and infections.

Along with deaths, these illnesses are also estimated to lead to the most hospitalizations. NTM infections are estimated to cause the most fatalities and hospitalizations.

What is recreational water illness?

Recreational water illnesses are spread by swallowing, inhaling or having contact with contaminated water in swimming pools, hot tubs, water parks, water play areas, interactive fountains, lakes, rivers, or oceans.

According to the CDC’s National Outbreak Reporting System, recreational water illnesses were responsible for 50% or more of reported waterborne illnesses from 1995 to 2021, except for 2017, 2019, and 2020.

Recreational water can be contaminated with pathogens and chemicals that cause various illnesses, including gastrointestinal, skin, ear, respiratory, eye, neurologic, and wound infections. Some common pathogens found in recreational water include:

• Cryptosporidium
• Pseudomonas or “hot tub rash”
• Leigonella
• Shingella
• Norovirus

“Hot tub rash,” also caused by pools and lakes, results from contaminated water that stays on skin for an extended time. The germ that causes contamination is called Pseudomonas aeruginosa and originates in water that is not properly disinfected with chlorine or falls outside of the recommended pH level of 7.2–8.

Shingella germs come from fecal matter such as diarrhea and is spread by swimming in, or swallowing, contaminated water. It can also be spread by encountering fecal matter in other ways, such as through changing diapers, sexual contact, or eating food prepared by someone who has a Shingella infection.

How can waterborne illnesses be prevented?

The CDC recommends that individuals prevent waterborne illnesses at home, and while camping, hiking, and traveling, and backpacking by practicing safe measures like keeping water infrastructure maintained and treating and purifying water correctly. Waterborne illnesses can be prevented at industrial and commercial levels by implementing safety standards. 

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