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Pool Microbiological Monitoring

Certain infections have been associated with the use of swimming pools and spa pools. These usually result from poor management of water treatment leading to the survival of pathogenic organisms introduced by pool users.

Cryptosporidium is the only organism of pathogenic significance that can withstand properly treated pool water. However, as pool water can provide optimal conditions for growth, other microorganisms of environmental origin can multiply in poorly managed pools. Most organisms capable of living in water grow best at temperatures between 20˚C and 45˚C. Those normally associated with the human body grow well at 37˚C. Most pool bacteria tests are incubated at 37˚C for this purpose. Each viable bacterium multiplies to form a colony and is therefore called a colony-forming unit (CFU). Bacterial results are reported as CFU per millilitre or CFU per 100 mL of sample (CFU/mL or CFU/100mL).

Microbiological monitoring for pool operators is a quality assurance activity. Good water treatment practices and control of critical physical and chemical parameters is quality control. Microbiological standards for pools are used by health authorities to establish the seriousness of non-compliance with chemical parameters and identify causes. A short-term fall in chlorine residual may not be enough to allow the growth of Pseudomonas or rise in plate count within pool water. Such growth may be present if a pool was not chlorinated adequately over many hours or days.

Deficiencies in microbiological parameters resulting from poor management practices can contribute to serious illness and are grounds for prosecution by health authorities.
Frequent monitoring of chemical parameters is necessary to ensure that critical limits of disinfection are not breached. Close attention to filter performance is also required.
Microbiological problems should be insignificant in a well-managed pool with an adequate disinfectant residual, a pH maintained at the recommended level and regular filtration and backwashing.
When occasional, minor deviations from the Regulatory limits occur and are identified and corrected promptly, health or water quality problems seldom occur.

Best Practice Model
• Only pool operators who have a microbiological sampling program can achieve verification of the effectiveness of their everyday quality control parameters.
• The frequency of monitoring should reflect the relative microbiological risk that each type of pool presents. Quarterly monitoring is regarded as sufficient for most pools.
• Where there is a significant deviation in disinfection below regulatory limits microbiological tests should be undertaken and the data recorded for future reference.
• Where microbiological samples do not comply with accepted Standards, re-sampling should be undertaken to ensure that corrective actions have been effective in restoring microbiological quality.
• Document all observations, results and findings.

All pools are required to be closed while chemical and physical parameters are outside Regulatory limits.
Occasionally, microbiological problems develop in pools because there is poor circulation and turnover caused by design inadequacies. These may occur in certain parts of the pool, such as entrance steps, which are cut away from the side of the pool. When there is a gathering of colloidal matter or a lowering of chlorine levels in these areas, microbiological contaminants may be present and pool operators should satisfy themselves that the water treatment regime is satisfactory by conducting microbiological testing.

Appropriate Microbiological Testing
Microbiological samples should be submitted for analysis at a laboratory that is NATA accredited for the particular tests required.

Assessing Microbiological Quality
Taken together, the standard plate count test, the coliform test and Pseudomonas aeruginosa test provide the simplest means of assessing the microbiological quality of swimming pool water.
Chemical parameters, such as pH, disinfectant residual, ORP, TDS and cyanuric acid, should be tested and recorded at the time of sampling. Any other relevant observations, such as bather loading or plant failure, should be noted.

Standard Plate Count
The standard plate count grows a number of different bacterial species without differentiating between them. It gives a good indication of the overall bacterial population within the pool environment. The result is normally reported as colony forming units per millilitre of water (CFU/mL). A standard plate count of less than 10 CFU/mL and the absence of coliforms and Pseudomonas aeruginosa can be expected from most well-managed pools.
A standard plate count in excess of 100 CFU/mL clearly indicates that operating conditions are unsatisfactory and require investigation—regardless of the disinfectant used. It may be related to filter performance or physical matter present in the pool.

Coliform Count
Coliform bacteria, particularly Eschericia coli (E. coli), are normal inhabitants of the intestinal tract of humans and other warm-blooded mammals where they are present in great numbers.
The coliform test is extremely important in assessing the immediate efficacy of the disinfection process, especially when bathers are using the pool at the time of testing.
If coliforms are found to be present there is likely to have been a serious failure in the disinfection process at the time of sampling, and a risk of gastric illness to pool users from bacteria and viruses found in the intestines.

Pseudomonas Aeruginosa
Pseudomonas aeruginosa is a pathogenic organism and often the cause of ear and skin infections, particularly folliculitis. Pseudomonas is an inhabitant of drains and slimes and can often colonise in filter media, particularly where there is not frequent backwashing, superchlorination or other oxidising processes that penetrate the filters. The presence of Pseudomonas may indicate the possible presence of other environmental pathogens, such as Legionella, which, if unchecked, can thrive in warmer pools.
Other Organisms
Provided satisfactory results are obtained for these three specified tests, it is not recommended that other organisms be routinely tested unless a particular health problem has been associated with a pool.
Staphylococcus is often found where pool users are present and its distribution within the water tends to favour the surface. It is associated with flaking skin, dandruff and nasal secretions because chlorine sometimes cannot immediately penetrate some particles. Staphylococcus is further controlled by effective water removal at the surface by skimmers and spill gutters and subsequent filtration.
Cryptosporidium is an issue of importance to the pool operator. It is a complex issue as it has wider implications to pool management.

Health authorities may be required to sample pool water and test for specific pathogens when investigating specific illnesses. Generally, in the absence of notified cases, testing for other organisms other than required by the Regulations is unwarranted. Pool operators should seek advice from the public health authority prior to taking samples for specific pathogens.