Pool Contamination and Disease Transmission


Often, the treatment of swimming pools poses more complex problems than those associated with drinking water. Pool sanitation begins with bather supervision and discipline. For the most part, the rules governing good conduct and cleanliness are common‐sense. This however does not detract from their seriousness and or the need for their strict enforcement.

It is important that all pool patrons be required to comply with Operator imposed Rules and Regulations. As a simple example of the potential risks and issues, an obviously healthy patron wearing a small bandage might seem to present an entirely harmless situation to an untrained Pool Operator. The bandage might cover the most common pimple or sore, yet the affected area might well have festered with staphylococcus bacteria. As a highly localized infection it presents no serious problem to the person afflicted, but it poses a significant health hazard if these same bacteria are washed from the infection and ingested or otherwise taken in by other bathers.

Pre Showering

Allowing patrons to enter the pool un‐bathed can impair the efficiency of the disinfection system by as much as 50%. Similarly, allowing patrons to swim whilst fully or partially clothed, will also create additional and unnecessary loading as will nontoilet trained infants. Pool policies that encourage patrons to shower prior to pool entry, encourage the use of swimming clothes or bathers and exclude all non‐toilet trained infants (without proper waterproof swimming pants) are important.

Whilst pre‐bathing may be difficult to enforce, the Operator has opportunities, by signage and general bather education, to emphasize the need for patrons to apply common sense and have due regard for the welfare of other bathers. It is unrealistic to expect that any treatment system will totally solve or eliminate every conceivable problem ‐ the majority of dirt load is (after all) carried into the water primarily by the bathers. Management of incoming dirt load must be properly managed at its source.

The most effective pre‐showering occurs where bathers use warm water and soap. The benefits of pre‐showering are therefore limited where only cold water is available and it is even more important that the Operator rigorously enforces thorough preshowering.

Since the contamination of the swimming pool water is inevitable, some methods must be provided to treat the water and make it safe for swimmers. Such treatment is accomplished by the operation of three inter‐related and interacting systems:‐

i. An effective means of recirculation and mixing of both the dirt load and or any chemicals that are added to the pool for sterilization and or water balance.

ii. An effective system for the removal of particles by filtration.

iii. An effective chemical dosing system.

Disease Transmission

It is essential to recognise that disease transmission (even in the best operated pool) is possible. At best, disease transmission can only be minimised. It takes some time (depending on the type of disinfectant, its concentration, contact time with the pathogen, water temperature and several other factors) for a disinfectant to kill microorganisms.

There is no such thing as an ‘instantaneous kill’, The Pool Operator has a fundamental requirement to maintain specific and minimum disinfection levels that will assist in the prevention of disease transmission. Such levels are confirmed within all State and Territory health regulations and reinforced by other codes.

Public pools are more likely to be contaminated with a greater diversity of disease causing organisms than single domestic swimming pools because public pools are used by unrelated people and are subject to higher bather loads. Disease causing organisms (pathogens) may be introduced from many sources but are predominantly associated with bathers. These organisms can be brought into a pool on the bathers’ skin, and in their saliva, urine and faeces.

Organisms can also be introduced from dust, bird droppings and soil carried on bathers’ feet. Some of these pathogens live and may even grow in pool water, unless the pool water is properly and continuously disinfected.

The most commonly known micro‐organism capable of causing large outbreaks in public swimming pools is Cryptosporidium. Outbreaks of cryptosporidiosis are a problem in public swimming pools because Cryptosporidium is chlorine resistant and it is easily transmitted by infants who are not toilet‐trained.

Cryptosporidium is a protozoan parasite, which causes a diarrhoeal illness called “cryptosporidiosis.” The Cryptosporidium parasite invades and multiplies in the gastrointestinal tract of infected cattle, sheep and humans, causing illness and producing Ocysts, the infective form of the parasite. Ocysts pass out in the faeces to the environment, where they can survive for a long time. They can also comfortably survive in water as Ocysts are resistant to the standard level of chlorine (used for pool disinfection),

Cryptosporidium in a public swimming pool poses a serious public health risk, particularly to children and immune‐compromised persons. Cryptosporidiosis transmission is faecal‐oral, including person to person, animal to person, waterborne and food borne transmission. This parasite is responsible for the majority of reported outbreaks of illness related to swimming pools because the Ocysts of Cryptosporidium Ocysts are chlorine resistant and extremely small (4‐6 microns).

Sand filtration does not possess the particle selectivity to detain and effectively remove all of the Ocysts from pool circulation quickly. Natural UV (sunlight) if present in sufficient quantity is an important element in the control of cryptosporidium as is proper maintenance of disinfection levels. However, the best defence against cryptosporidium and most other pathogens is to prevent them from entering the pools in the first place.


i. Outbreaks of disease are usually linked to inadequately disinfected swimming pools.

ii. Whilst only “outbreaks” seem to be reported, many other single cases go unreported.

iii. Management of incoming dirt load must be properly managed at its source, preferably by a strictly enforced policy of pre showering.

iv. Even if a swimming pool is properly managed and adequately disinfected, disease transmission can still occur by risky or adverse behaviour such as:

• Spitting, nose blowing, etc.,

• Faecal accidents and poor fitting toddler pants,

• Poor personal hygiene

• Not toileting before entering the pool.

v. Despite any apparent water quality, swimming pools should never be considered as being a sterile environment.

vi. Whilst contaminants are being constantly added by bathers, at least one to two minutes of contact time is needed to disinfect the contaminants once they enter the pool. Cryptosporidium is an exception whereby its removal or destruction can take several days.

vii. It is essential for pool patrons to minimise pool contamination and to avoid risky behaviour.

Pool Operators should never allow disinfectant concentrations to fall below recommended levels and should anticipate high bather loads and raise disinfectant levels accordingly. Automatic water chemistry controllers cannot anticipate demand and therefore Operator involvement is essential.

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