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Managing Legionella Risks in Dental Practices

All healthcare facilities must manage and control the risks associated with the safety of water used. The quality of water must conform to current guidelines to prevent contamination by harmful microorganisms that may potentially colonize these systems.

Dental practices are no different. The control of cross-infection and cross-contamination in dental practice is the focus of continuing discussion and debate.

Dental Unit Water Lines (DUWL) can become contaminated by oral and environmental microorganisms and microbial biofilm and this can be a potential source of cross-infection for patients and staff.

Whilst the reported incidents of legionella are low, registered managers of dental practices must be prepared to safely manage and control the risks of legionella outbreak in their premises.

Why are dental practices at risk of legionella outbreak?

Legionella bacteria are ubiquitous in nature and commonly colonise dental chair units (DCUs) and DUWL, water storage tanks, hot and cold water distribution systems, handpiece lines, scalers and air-water syringes including cuspidor. Where conditions are right the bacteria can multiply to significant numbers and present a risk.

Bacterial contamination of DUWL is believed to originate in the DCU water supply which usually contains low levels of microorganisms. The main reason for the extensive contamination present in DUWL is the complex waterline network within DCUs. This network consists of several metres of tubing with a narrow internal diameter in which water can stagnate when the equipment is not being used.

Microorganisms in water entering the DCU water supply attach to the internal surfaces of the waterlines where they form microcolonies and eventually give rise to multispecies biofilms.

Biofilm forms because the water at the edges of the narrow-bore DUW tubing flows more slowly than water at the centre of the tubing and thus there is little or no disruption to the microorganisms present on the inside surface of the waterline. Contact with surfaces also causes the bacteria to become more adhesive.

Biofilms once built up are very difficult to remove and penetration of disinfectants into biofilms is problematic.

How do people contract Legionnaires’ disease in dental practices?

The presence of high densities of microorganisms in dental unit water is a potential risk of infection for dental patients and staff and is incompatible with good hygiene and cross-infection control and prevention practices.

Dental staff and patients can inhale contaminated water droplets that are generated by dental instruments such as the high-speed handpiece or ultrasonic scaler.

The use of masks can provide limited protection from aerosol for dentists and members of staff, but the aerosols generated can easily be inhaled by the patient who has no barrier protection.

DUWL contamination is of particular concern in the treatment of immunocompromised and medically compromised individuals.

Therefore, it is essential to ensure that the water used during dental procedures is of a quality that does not pose any threat or risk to health to either staff or the patient.

Legislation & Guidance

Measures are required by law to manage the risk of Legionella exposure for workers as outlined in is The Safety, Health and Welfare at Work Act 2005 (S.I. No. 10 of 2005).

Dentists must take appropriate precautions to protect their patients and their staff from the risk of cross-infection.

Failure to provide and use adequate decontamination, disinfection and sterilisation facilities may lead to proceedings for professional misconduct before the Fitness to Practise Committee of the Dental Council.

If a healthcare organisation is prosecuted for a breach of health and safety law, and it is held that it did not follow the relevant provisions of the Code, that organisation would need to demonstrate that it had complied with the law in some other way, or a court would find it at fault.

All premises are required to have a written scheme and a legionella risk assessment for controlling any identified risks in accordance with HSE’s guidelines.

In Ireland, HPSC National Guidelines for the Control of Legionellosis in Ireland, 2009 is the principle document defining the controls required in respect to the risks from legionella bacteria.

HPSC recommends reading these guidelines in conjunction with the UK Health and Safety Executive’s Approved Code of Practice L8.

ACOP L8 is “aimed at duty holders, including employers, those in control of premises and those with health and safety responsibilities for others, to help them comply with their legal duties in relation to legionella.

The primary focus of ACOP L8 covers the following important areas:

  • Legionella risk assessment
  • The role of the appointed competent person, known as the “responsible person”
  • The control scheme for legionella risks
  • Reviewing control measures and record-keeping
  • The duties and responsibilities of those involved in the supply of water systems

There is specific guidance on the care of dental unit water lines in the UK Government’s Health Technical Memorandum 01-05 (HTM 01-05) which is intended to raise the quality of decontamination work in primary care dental services by covering the decontamination of reusable instruments within dental facilities.

How to control the growth of legionella bacteria in dental practices?

Numerous suggestions for reducing the bacterial density in dental unit output water have been proposed but none have been universally accepted which are both efficient at eliminating biofilms, as well as being safe for patients.

One widely used practice for reducing the bacterial density in dental unit output water involves flushing DUWL with water. However, Flushing DUWL at the start of the clinical session to reduce the microbial density in output water does not affect waterline biofilm or reliably improve the quality of the output water used during dental treatment.

Using tap water, distilled water or sterile water in a self-contained bottle reservoir system will not eliminate bacterial contamination in output water if waterline biofilms are not effectively controlled.

The most efficient means of maintaining good quality DUW output water is regular disinfection of DUWL with a disinfectant or biocide that removes biofilm from the waterlines resulting in output water of potable quality.  Following disinfection, all of the waterlines should be thoroughly flushed to eliminate biocide.

Dental practitioners should seek advice from the manufacturer of their dental unit or water delivery system to determine the most appropriate method for maintaining acceptable output water quality.

Biofilm regrowth can occur within a week or so following disinfection and so DUWL should be disinfected at least once weekly with an appropriate disinfectant.

Microorganisms, blood and saliva from the oral cavity can enter the dental unit waterline system during patient treatment. Thus handpieces, ultrasonic scalers and air/water syringes should be operated for a minimum of 20 to 30 seconds after each patient to flush out retracted material.

Written or electronic records of weekly waterline disinfection, equipment maintenance and periodic waterline cleaning efficacy testing should be retained.

Legionella Risk Assessments for Dental Surgeries & Practices

To comply with the health & safety laws and fulfil the requirements of HPSC’s guidelines, all dental practices must perform a legionella risk assessment to identify potential hazards relating to exposure to legionella bacteria from their water systems.

It is the responsibility of the duty holder to ensure a risk assessment is in place and reviewed periodically but it must be undertaken by a competent person.

ACoP L8 & HPSC’s National Guidelines for Control of Legionellosis in Ireland tell us that this person should have the ability, experience, instruction, information, training and resources to be able to carry out the work and should know:

  • The potential sources of legionella and the risks they present;
  • Measures to adopt, including the precautions to take to protect the people concerned, and their significance;
  • Measures to take to ensure that the control measures remain effective, and their significance.

Assessments are necessary periodically, and water samples should be taken to further aid the analysis of the water quality. Records must be kept of routine checks, cleaning and disinfection as part of a legionella management programme.

Book a Consultation

Celtic Water Solutions is a leading water hygiene service provider in Ireland offering a complete range of services including legionella testing, risk assessment, any remedial works needed, ongoing monitoring for tasks, and water tank cleaning.

Our risk assessments have been developed in accordance with the guidelines and recommended practices issued by the HPSC’s National Guidelines for Control of Legionellosis in Ireland and UK HSE’s ACOP L8.

If you are a dental practitioner or run a dental practice, feel free to speak to our consultants for more information.
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