Water Sanitation Health

Guidelines for safe recreational water environments
Volume 1 : Coastal and fresh waters

Executive summary


Free-living microorganisms

In addition to microorganisms introduced to recreational waters through human or animal faecal contamination, a number of pathogenic microorganisms are indigenous to such areas or, once introduced, are capable of colonizing the environment.

Vibrio species are natural inhabitants of marine aquatic environments in both temperate and tropical regions. The occurrence of vibrios does not correlate with the occurrence of the traditionally used bacterial faecal index organisms, except perhaps in waters receiving human wastes from disease outbreaks (mainly cholera). Due to the ubiquitous nature of Vibrio species in the aquatic environment, their presence in bathing water cannot be controlled by water quality control measures such as wastewater treatment and disinfection. Human carriers and shedding appear to be of only limited importance in the epidemiology of Vibrio infections associated with recreational water use. For V. cholerae, 106 organisms or more are typically needed to cause cholera, so that it is unlikely that persons bathing or involved in other recreational water activities would ingest vibrios in numbers high enough to cause gastrointestinal disease. However, the risk of extraintestinal infections associated with human pathogenic Vibrio species, especially wound and ear infections, during recreational activities in water is of health importance, although the infectious doses for such infections are unknown.

Aeromonas spp. are considered autochthonous inhabitants of aquatic environments and are ubiquitous in surface fresh and marine waters, with high numbers occurring during the warmer months of the year. Clinical isolation of these microbes presents the same seasonal distribution. Numbers may be high in both polluted and unpolluted habitats with densities ranging from <1 to 1,000 cells per ml. Sewage can also contain elevated numbers (106-108 cells per ml) of aeromonads. Aeromonas has been found to have a role in a number of human illnesses including gastroenteritis. Cases of wound infections in healthy people associated with recreational water have been described, as have cases of pneumonia following aspiration of contaminated recreational water.

Free-living amoebae are unicellular protozoa common to most soil and aquatic environments. Of the many hundreds of species of free-living amoebae, only members of the genus Acanthamoeba, Naegleria fowleri and Balamuthia mandrillaris are known to infect humans, often with fatal consequences. Acanthamoeba have been isolated from natural and artificial waters. Certain species are pathogenic to humans and cause two clinically distinct diseases affecting the central nervous system: granulomatous amoebic encephalitis (GAE) and inflammation of the cornea (keratitis). Naegleria fowleri, which is found in thermal freshwater habitats worldwide, causes fatal primary amoebic meningoencephalitis (PAM) in humans. PAM is usually fatal, with death occurring in 3–10 days after exposure. Infection usually results from swimming in contaminated water, although the infectious dose for humans is not known. B. mandrillaris encephalitis is largely a disease of the immunocompromised host, and certain cases of GAE attributed to Acanthamoeba have in fact been shown to have been caused by B. mandrillaris.

Leptospires are excreted in the urine of infected animals, which can then contaminate soil, mud, groundwater, streams and rivers. Humans become infected either directly through contact with infected urine or indirectly via contaminated fresh water or soil. Virulent leptospires gain entry to the body through cuts and abrasions of the skin and through the mucosal surfaces of the mouth, nose and conjunctiva. In cases due to exposure to recreational water, the incubation period seems to vary between 2 and 30 days, but generally is between 7 and 14 days. The clinical manifestations of leptospirosis vary considerably in form and intensity, ranging from a mild flu-like illness to a severe and potentially fatal form of the disease, characterized by liver and kidney failure.

Evidence suggests that although infection with free-living microorganisms or pathogenic leptospires via recreational water use may be life-threatening, the incidence of such infection is very low and, in many cases, is limited to specific areas. As such, no specific guideline values have been recommended, although authorities should be aware of the potential hazards posed by these organisms and act accordingly. Assessment of the likely hazard (e.g., the likelihood of thermal warming of fresh waters) and education of water users and health professionals are important control measures.

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