Bacteria Hazards of Swimming in Freshwater Lakes and Ponds

What could be more refreshing on a hot summer day? A dip in the local lake or pond is just the ticket for relief from the heat and humidity. Even if the water looks clear, clean and inviting, what you view as a reprieve from intolerable heat may also be viewed as nirvana to the local bacteria and germ population. With the worldwide popularity of water recreation, Recreational Water Illness (RWI) education and prevention is now a focus of the Centers for Disease Control in the United States and the World Health Organization internationally.

A variety of microorganisms are naturally present in soil and water in the environment. Bacteria are part of this environmental stew. They are also part of the digestive systems of many living organisms, including humans. They keep nature in balance with their ability to decay material and provide food for others. Without bacteria, life would cease on the planet. But some of these bacteria are truly nasty to humans.

Bacteria are one-celled microorganisms that thrive in a variety of environments. They come in many different sizes, shapes, preferred temperatures, and oxygen requirements. The true number of species of bacteria is unknown but is estimated to be between 10 million to one billion species in the wild.

While bacteria can be beneficial, they can also pose a serious and potentially fatal hazard to those who swim in ponds and lakes. Many of the world's best-known disease outbreaks have been transmitted by water-borne bacterium. That refreshing lake or pond is essentially untreated drinking water and swarming with unseen microorganisms. If you accidentally ingest, inhale, or come in contact with some of these microorganisms, you may have a memento of that dip in the lake for weeks to come.

How did bacteria get into the lake or pond?
There are a number of ways that bacteria can get into the water. Domesticated animals and wildlife feces contain millions of bacteria. Periods of significant rainfall will wash bacteria from the feces and those in the soil into ponds and lakes. Additional sources of contamination can come from sewage spills, animal waste, and from infected swimmers. A small amount of feces can quickly contaminate a recreational body of water.

How can they infect people?
Bacteria have several routes of infection. They can be swallowed, you can breathe them in, or they can come in contact with an open wound. One drop of untreated water can contain millions of bacteria. It is possible to develop skin infections, ear infections, eye infections, diarrhea, and respiratory infections from contaminated lake water.

Who is at risk?
Everyone can be at risk however pregnant women, children, and those with a compromised immune system may experience more severe sickness when infected. Tourists may be vulnerable to unknown local endemic diseases and can develop severe illness. (1,2) Many of these bacteria do not have to be consumed in large quantities to produce illness.

What bacteria can I be exposed to in contaminated lake water?
There are a number of pathogenic bacteria that can be found in lakes and ponds in the USA and around the world. The following species are ones that can be found in USA bodies of recreational water and internationally. (1,2)

Vibrio cholerae - This bacteria is responsible for cholera outbreaks worldwide. While no longer common in the United States, it is still a concern when visiting countries with epidemic cholera. (3)

E. coli O157:H7 - Found worldwide, this bacterium produces a bloody diarrhea. It is also a serious concern in food contamination. It may only take 5 to 50 organisms to become infected. Children and the elderly are at high risk of severe illness. Many documented cases of RWI caused by E. coli 0157:H7 have been documented in the United States and the United Kingdom. It has also been found in swimming pools in both countries. (1,2)

Shigella - There are four species found worldwide. It produces a bloody diarrhea. It is transmitted by contaminated food and sewage contaminated water. One species, S. dysenteriae is responsible for over1.1 million deaths annually with most cases occurring in children of developing countries. It only takes between 10 to 100 organisms for infection. Shigellosis caused by water recreation is low but major outbreaks have been documented in the United States. Most infections by S. sonnei and S. flexneri occurred while wading, swimming underwater, and swallowing water. (1,2)

Campylobacter jejuni - Found worldwide, it produces an infective diarrhea in its victims. It is the most commonly found infective diarrhea in industrialized countries. It is usually transmitted by water contaminated by animal feces. (2)

Leptospirosis - It has worldwide distribution. Its mild forms range from barely detectable to severe muscle pain. Its severe forms are often fatal if left untreated. It is commonly transmitted by water contaminated by animal urine or soil that comes in contact with open wounds. Infection can occur while swimming, wading, or rafting. It only takes one to ten leptospires to cause a fatal infection. Upon entering the host, leptospires can spread quickly into the bloodstream. If left untreated leptospires can eventually enter the kidneys, brain, and the eye. While found more commonly in tropical countries, documented RWI cases have been recorded in Illinois, Ireland, Wales, and England.(2)

Salmonella & Typhoid fever - It has worldwide distribution with a variety of species. It is spread by feces contaminated water and food. Over the past thirty years there has been a rise in salmonellosis in Europe. There is also an increasing incidence of multi-drug resistant Salmonella. Salmonellosis has been documented in the United States and the United Kingdom with the highest incidence in summer. Most infections are mild except those by Salmonella species S. typhi and S. paratyphi. Infections by these species cause Typhoid fever and paratyphoid fever. Around 100 cases of typhoid fever are documented annually in the United States. Most cases of non-typhoid salmonellosis are from food but a few are linked to recreational water usage. Depending upon species it can take between 10 and 10,000 organisms to become infected. (2)

Helicobacter pylori - It is found worldwide but the infection mode is unclear. It is linked with RWI but more studies need to be performed. It is also responsible for some gastric ulcer formation. (2)

Legionella - Found worldwide, it produces legionellosis. It is usually transmitted by naturally occurring Legionella or water contaminated by human sewage. Humans can be infected by as little as one organism. While more commonly contracted from hot tubs, documented cases exist of infection from swimming in open water. (2)

Mycobacterium avium complex (MAC) - It has worldwide distribution with 16 species that associate with water. Transmission can be by inhalation, ingesting the organism, or through an open wound. It may also be a causative factor for Crohn's disease. It can take several thousand to several million organisms to become infected. Higher numbers of M. avium are found in bodies of water with little oxygen and high amounts of organic matter. Most documented infections are from hot tubs and swimming pools rather than lakes. (2)

What precautions should be taken so I don't get infected?
Steer clear of your favorite swimming hole after periods of rain. That's when large amounts of contaminants are flushed into bodies of water. It's best to swim in well-maintained private or municipal pools - never in cattle ponds or water troughs. That local lake may look good, but be teeming with harmful bacteria. Consult the local Health Department for any closures, warnings, or reports. If someone in your party is ill with diarrhea, ask them to avoid swimming until they are well.

Are there any other additional germs that I should worry about in lakes and ponds?
There are a number of other microorganisms that commonly contaminate lakes and ponds. Two viruses that inhabit water sources and are a concern to swimmers are norovirus, and rotavirus. Both can cause diarrhea. Parasites that can infect swimmers in the USA are giardia, Cryptosporidium, schistosomiasis (Puerto Rico), and E. histolytica amoeba (Amebiasis) (1, 4)

Swimming is a fun recreational exercise that provides relief on a sunny hot day. With the proper precaution and care it's an excellent way to enjoy the afternoon. Don't forget the sunscreen!

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Sources:
1. Centers for Disease Control, http://www.cdc.gov/healthyswimming/

2. Pond, Kathy. "Water recreation and disease. Plausibility of associated infections: Acute effects, sequelae and mortality" World Health Organization, 2005. p.59-146 http://www.who.int/water_sanitation_health/bathing/recreadis/en/index.html

3. Crun, et al, "Waterborne outbreaks reported in the United States". Journal of Water and Health, 2006 p19-30

4. - http://www.ahealthyme.com/topic/dysentery