By Kelly Reynolds, MSPH, Ph.D.

Levels of recreational waterborne disease is at the highest level since reporting began in 1978, suggesting the need for interventions aimed at reducing risks in natural and treated water systems. More outbreaks are reported related to recreational waterborne disease than drinking water sources. Every two years the Centers for Disease Control and Prevention (CDC) publishes a report on waterborne disease outbreaks in the US. These surveillance summaries provide the single most complete source of data on documented drinking and recreational waterborne illnesses since 1971 and 1978, respectively. The most recent surveillance summary (Yoder et al., 2008) describes 78 reported recreational water outbreaks from 2005-2006, some with fatal consequences.

Recreational Waterborne Disease
From 2005-2006, 31 states in the US reported a total of 78 outbreaks due to recreational water exposure. The source of exposure is most commonly ingestion (61.5 percent) but inhalation (12.8 percent), direct skin contact (10.3 percent), and mixed exposure routes (11.5 percent) and other (3.8 percent) are also confirmed. Events range from cases of enteric illness, respiratory ailments, skin infections and irritations, hospitalization and death. Of the 4,412 persons reporting illness, 116 were hospitalized and five people died. The causative agents in recreational waterborne disease are as varied as the exposure route, however several trends are notable: 1) the majority of outbreaks (61.5 percent; 48/78) were due to gastroenteritis following exposure to either infectious microbes or chemicals; 2) the majority of outbreaks (74.4 percent; 58/78) occurred in treated water venues and 3) most were caused by the protozoa, Cryptosporidium (see Figures 1 and 2).

Cryptosporidium has been in the headlines before, causing the largest waterborne outbreak in modern US history in Milwaukee, Wisconsin in the 90s. In this outbreak, 50+ people died and 400,000 cases of illness were reported. Resistant to chlorine disinfection, Cryptosporidium altered our focus for drinking water treatment to include ultraviolet light or filtration. A single outbreak of Cryptosporidium at a spray park in New York resulted in over 2,000 cases of illness, mostly among young children.

Other causative microbial agents of recreational waterborne disease from 2005-2006 include: Norovirus, Giardia, Naegleria, Leptospira, Vibrio spp., Campylobacter jejuni, Shigella sonnei, Pseudomonas aeruginosa, and Legionella. Two outbreaks from exposure to excessive amounts of copper sulfate in a lake and liquid chlorine/muriatic acid in a swimming pool were also documented. For 12 outbreaks (15 percent) a causative agent could not be identified, although for most, a microbial pathogen was suspected. An understanding of etiologic agents involved in recreational waterborne disease is important for appropriate monitoring, intervention and control.

Regulating Recreational Waters
Recreational water may be defined as swimming or wading pools, hot tubs or spas, water slides, interactive fountains, wet decks and natural bodies of water (fresh or marine water environments). Therefore water sources may be treated using filters and/or disinfectants or they may be completely untreated source waters.

US EPA has a long history of setting guidelines for natural recreational waters, including rivers, lakes and oceans but state and local governments are responsible for setting and enforcing regulations aimed at protecting the quality of these recreational waters. In 1986, the agency recommended limits for indicator bacteria (E. coli) that states could adopt directly or improve upon. E. coli is a fecal indicator bacteria commonly used in the drinking water, food, and recreational water industries to monitor food and water quality. The presence of E. coli indicates fecal contamination and the potential for other harmful enteric bacteria, viruses and protozoa to be present. While the E. coli test provides a quick and easy tool to monitor water quality, the ability of the bacterium to regrow in the environment and conversely to die off long before some other human pathogens of concern, means that the true health risk relative to an E. coli count is uncertain. In temperate climates where E. coli readily grows, other bacterial indicators are often recommended (i.e., enterococci).

States and territories that have not developed their own standards from the US EPA recreational water quality guidelines are now held to recently-established federal standards. The allowable number of E. coli in natural waters is dependent on the level of human contact expected. For example, for full body contact in a freshwater source, the monthly geomean of E. coli or enterococci must be below 126 or 33 colony forming units (CFU; i.e., culturable) bacteria per every 100 ml of water, respectively. In marine waters designated for full body contact, enterococci indicators are preferred and must be below 35 CFU/100 mL. More polluted waters may be designated for other recreational activities not related to full-body contact, like wind surfing or boating.

Interestingly, no federal guidelines exist for swimming pools and other treated recreational waters related to treatment, thus state or local health departments set and enforce swimming pool codes that vary widely by region. The CDC is working on the development of the Model Aquatic Health Code (available at in an attempt to standardize pool codes across the nation.

Focused Controls
Controlling recreational water exposures can be difficult since often when a problem has been identified, people are already exposed. For natural waters, state and local authorities have the choice of what interventions to employ including closing a venue or posting signs to increase risk awareness. In the case of Naegleria fowleri, avoiding exposure is difficult since this free-living amoeba is naturally present in freshwaters, particularly during warm weather events when algal growth increases. Naegleria fowleri infections are almost always fatal, with three fatalities occurred in the 2005-2006 survey period, but controlling this organism in the water is not an easy task.

Other contamination events may be preventable. US EPA has developed an action plan for beaches and recreational waters called Beach Watch aimed at extending protective programs to keep waters clean. Other studies are underway to improve monitoring methods to better correlate with health impact estimates.

While natural waters offer many challenges, swimming pools have the advantage of being a contained source that could be more readily controlled. Proper control of chemicals and pH is important for maintaining the chemical and microbial balance of pools that might otherwise lead to skin irritations and infection with chlorine-sensitive pathogens. However, ingestion of water contaminated with chlorine-resistant Cryptosporidium remains a major concern even in pools that are well maintained.

Cryptosporidium cases have nearly doubled since 2004. Alternative treatment technologies must be utilized to reduce outbreaks of Cryptosporidium from swimming pools. Ultraviolet light and ozone disinfection are both effective where traditional chlorination and filtration fail. The CDC identifies other risk reduction steps: increased circulation flow rates, flocculants, biocidal shock treatments, and water replacement regimens (Yoder et al., 2008). Outbreak data indicates that persons recreating are a major source of contamination where improved hygiene and education may provide a significant reduction in illness rates.

Many data gaps exist relative to recreational waterborne diseases. Not all etiological agents are identified in outbreaks and outbreaks are known to be only the tip of the iceberg relative to the true burden of disease from recreational water. There are many possible reasons for the 2005-2006 survey period being the highest on record for outbreak occurrence. The emergence of pathogens, like the chlorine-resistant Cryptosporidium is one reason but improved awareness and reporting may also be key factors.

Communal swimming conjures up the image of fecal tea bags where individuals swimming during diarrheal illness contribute to a much stronger tea. Ingestion of water during swimming is common and those involved in more extreme activities that include head submersion, are at increased risk by ingesting more than others. Public education is needed to stress that one should not swim when ill and that fecal accidents should be reported and immediately addressed to minimize further illness.


  1. Yoder, JS, MC Hlavsa, GF Craun et al., 2008. Surveillance for waterborne disease and outbreaks associated with recreational water use and other aquatic facility-associated health events— United States, 2005—2006. CDC-MMWR Surveillance Summaries. 57(SS09); 1-29.

About the author
Dr. Kelly A. Reynolds is an associate professor at the University of Arizona College of Public Health. She holds a Master of Science degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds has been a member of the WC&P Technical Review Committee since 1997. She can be reached via email at [email protected].


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