According to Public Health England (formerly known as the Health Protection Agency) Pseudomonas aeruginosa is one of the
more common causes of healthcareassociated infections, with between 3,700 and 4,000 reported cases each year. The increasing resistance of these bacteria to many antibiotics makes their control and removal a top priority for infection control managers. In hospitals the organism contaminates moist/wet reservoirs such as respiratory equipment and indwelling catheters. In dental surgeries, dental unit water lines provide a perfect environment to harbour the bacteria, with the potential to cause infections in vulnerable patients.
In recent years, Pseudomonas aeruginosa infections have been responsible for a number of fatalities including the deaths of three babies in January 2012 at Belfast’s Royal Jubilee Hospital. As part of the report into this outbreak published in May 2012, the Regulation and Quality Improvement Authority (RQIA) concluded that the outbreak was most likely linked to
contaminated tap water in the intensive care rooms of the affected neonatal units and made a recommendation for the immediate implementation of a water management action plan.
Eradicating infections and diseases caused by contaminated water supplies is a constant consideration and challenge for dental practices, due to the nature of water delivery systems used in modern day treatment centres. In February 2011 an 82 year-old Italian woman died from Legionnaires’ disease, linked to the discovery of high levels of Legionella pneumophila in
the dental unit water lines at her local dental practice.
Legionella occur naturally in water, usually in low numbers, but in stagnant water they flourish, and can colonise water pipes, fire sprinkler systems, water containers for ice- making machines, humidifiers, water towers, air conditioning plants, showers and of course dental unit water lines.
The growth of Legionella is enhanced in the presence of biofilm, which is almost always present on the wall of water tanks and within the tubing that carries water from input to output source in the vast majority of dental treatment centres. Although the majority of the organisms in biofilm are harmless, there is potential for dental units to harbour opportunistic
pathogens.
Continuing cases, such as those referenced above, bring the quality of water dispensed into patients’ mouths via dental unit water lines into sharp focus. Although the issue is rarely raised by patients themselves, the duty of care and legal responsibility of dentists is to comply with regulations and guidance, that in England state that water quality should be at least that of European standards of drinking water, in other words between 100- 200cfu/ml.
There are three main options for cleaning dental unit water lines:
- Water treatment producing an oxidising biocide in situ – water is treated by electrolysis and the addition of reagents produces a biocide such as hypochlorous acid, which is fed directly or indirectly into the DUWL system.
- Addition of a biocide to the water fed to the DUWL – a reagent is added to the water in the bottle used to feed the treatment unit. This remains constantly in the water that is fed through the system to the patient.
- Regular off-line treatment with a biocide to remove and control biofilm – A biocide is added to the system when it is not in use. This may be left overnight or over a weekend and is flushed out with water before the system is used. During use no biocide is present in the water.
Aside from the disadvantage of requiring capital equipment for the first option listed above, there are also a number of practical disadvantages to using the second option of constant disinfection. Firstly, the biocide solution is in contact with the mucous membranes of patients with the potential of causing irritation/allergy/ingestion. Secondly, adhesion of materials to tooth surfaces may also be adversely affected by the presence of biocide formulation in the irrigation water. Finally the internal surfaces and mechanisms of hand pieces are in constant contact with the biocide, with the potential for corrosion or wear effects over time.
In addition, the continual presence of a disinfectant can give a false result when testing for bacteria as an indicator for the presence of biofilm. Water containing disinfectant, which is running through a contaminated system, may test as clean since the disinfectant may effectively kill the bacteria picked up from biofilm, without actually eradicating the biofilm itself. None of these disadvantages apply to an off-line biocidal treatment, which effectively removes biofilm.
If no preventive measures are undertaken, biofilm will readily form in DUWL and in addition to the water line system itself, any containers used for the storage of water and the bottles provided as reservoirs within the systems are susceptible to biofilm colonisation and should also be treated. In order to get meaningful test results, both the input and output water should be tested and compared to obtain a true idea of whether the waterline is free from biofilm of not.
The quality of water supply and storage conditions must be effectively managed in order to ensure that adequate output water quality can be achieved and the potential for formation of biofilm minimised.
The need for on-going testing of water quality is an important part of a practice’s infection control policy and regular monitoring using a reliable and accurate system is necessary to ensure water quality is maintained within acceptable levels. Normally, threemonthly testing is sufficient to monitor water quality and this can either be carried out using dip slides, an ATP based system or by sending samples of both input and output water to an external laboratory for microbiological testing (results are returned within seven days). Whichever testing method is selected, results should be recorded and available for inspection if required.
Ensuring water lines are free from biofilm and that this status is maintained is an essential part of infection control procedures. Although the presence of biofilm is not always obvious, its ability to harbour pathogens that can harm patients should not be underestimated and cautionary tales of infections and subsequent illnesses are widespread. Removal and on-going prevention of biofilm and its subsequent more deadly infections is simple to carry out and easy to monitor and in terms of safeguarding patients it is everyone’s duty to comply.
References available on request.