Merck Manual

Please confirm that you are a health care professional

honeypot link

Answering Patients’ Questions on Recreational Water Illnesses—Commentary

08/08/16 Larry M. Bush, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University|University of Miami-Miller School of Medicine;

A rise in media coverage of Zika and water sanitation issues at the Olympic Games has increased attention to water-related illnesses. Given the focus on and, perhaps, fear of the issues, physicians should expect to hear many more patients asking about the safety of the pools, beaches, rivers, and lakes they plan to visit this summer.

Patients can be reassured that water-related illnesses, specifically recreational water illnesses (RWIs) are far less common in the United States than in developing nations, where diarrhea is a leading cause of infant mortality. But that doesn’t mean there aren’t dangerous microorganisms lurking in U.S. waters. Recent reports of brain-eating amoebas and flesh-eating bacteria have already made headlines this summer.

In fact, RWI outbreaks related to swimming have been on the rise in the U.S., and prevention challenges remain. Cryptosporidium, the protozoan that causes a rare disease called cryptosporidiosis, is difficult to remove through conventional filtration and is resistant to chlorination; it can survive for days even in properly disinfected pools. New treatment issues have also arisen.

The effect of climate change on RWIs is also being studied. Research from the National Institute of Environmental Health Sciences concluded “although the United States has prevention and treatment strategies for waterborne diseases, surveillance is still spotty, diagnoses are not uniform, and understanding of the impact of climate change on these diseases is not well established.” More than half of waterborne disease outbreaks in the U.S. over the last 50 years have been associated with heavy rain, according to the Natural Resources Defense Council.

Answering patients’ questions

Patients need to be informed on the best ways to protect themselves from illnesses ranging from uncomfortable to life threatening. First, it’s important to ensure patients understand the different kinds of water-related illnesses and what they’re most likely to be exposed to. They are:

  • Water-based diseases in which animals in or near water (eg. fish, crustaceans, mosquitos) carry certain diseases.
  • Water-wash illnesses in which contaminated water is used in the cooking process.
  • Waterborne diseases that are caused by ingesting or absorbing water containing pathogenic microorganisms

Patients may ask one or several of the following questions if they are preparing for a trip involving recreational swimming or if they have recently returned from a similar outing.

Which waterborne illnesses am I most likely to be exposed to?

Here are five RWIs patients should be aware of:

  1. Giardiasis: Giardiasis is an infection with the flagellated protozoan Giardia intestinalis (lamblia). Found in fresh water, it’s the most common parasitic intestinal infection in the U.S. Giardiasis is known as beaver fever because it is commonly transmitted through the feces of beavers and other animals infected with Giardia. Even cool, clear mountain streams can harbor Giardia, so hikers must be wary.
  2. Shigellosis: Shigellosis is an acute infection of the intestine caused by Shigella. An estimated 500,000 people in the U.S. develop the infection every year as a result of water contaminated with human waste and inadequately chlorinated pools. Because individuals need only ingest a small amount of contaminated water to become infected, it’s common in pools and other areas in which there are many children.
  3. Vibriosis: Noncholera vibrios include Vibrio parahaemolyticusV. mimicusV. alginolyticusV. hollisae, and V. vulnificus. Patients can develop intestinal infection by consuming inadequately cooked shellfish (especially oysters) harvested from contaminated salt water or mixed fresh and salt water like bays. Individuals can also develop soft tissue infection if they cut themselves on a crustacean that harbors vibrio. Vibrio vulnificus, which thrives in warmer water temperatures, caused a number of deaths and amputations along the Gulf Coast of the United States this year.
  4.  Escherichia coli infection: E. coli are the most numerous aerobic commensal inhabitants of the large intestine. E. coli O157:H7 and other enterohemorrhagic E. coli (EHEC) typically cause acute bloody diarrhea, which may lead to hemolytic-uremic syndrome. Infection can be contracted by swallowing water that’s been contaminated by the stool of infected individuals, for example in public pools. Lakes and beaches occasionally close due to E. coli outbreaks.
  5. Primary amebic meningoencephalitis (PAM): PAM is a generally fatal, acute CNS infection caused by Naegleria fowleri. The amoeba lives in warm fresh water. PAM is rare; according to the CDC only 138 people have died as a result of PAM since 1962. Swimming in contaminated water exposes the nasal mucosa to the organism, which enters the CNS via olfactory neuroepithelium and the cribriform plate. Most patients are children or young adults.

WWho is most at risk for waterborne illnesses?

People who come in contact with contaminated water can contract waterborne illnesses, but individuals with compromised immune systems, people who have received an organ transplant, infants, the elderly, and pregnant women are at greater risk.

Where are waterborne illnesses most likely?

People are more likely to contract an RWI from fresh water than salt water. There are many organisms that cause RWIs, such as N. fowleri and Giardia, which thrive exclusively in fresh water. Additionally, pools, hot tubs, and other swimming environments where transmission is more likely are usually fresh water-based.

Does wearing goggles and keeping eyes closed underwater help prevent RWIs?

In general, eyes are relatively impervious to infections. Opening the eyes underwater does not increase the risk of contracting a RWI, and goggles are not necessary for protection.

How can people reduce the risk of contracting an RWI?

Provide patients headed to the pool, beach, or lake with the following general guidelines for avoiding RWIs:

  • Check the state’s official department of environmental protection website for updates on beach and water conditions.
  • Keep pools well treated with chlorine and keep fecal matter and other contaminants away from the water.
  • Avoid swimming in areas where there are babies wearing diapers or individuals with open cuts.
  • Avoid swimming if  you currently have diarrhea or have had it in the last two weeks.
  • Swallow as little water as possible.
  • Shower immediately before and after going in the water.

You can refer patients to the consumer version of the Merck Manual to give them a more accurate understanding of common RWIs and key steps to take before, during, and after swimming.