ORAL MICROBIOLOGY AND PRIMARY DENTAL CARE Risk Assessment of Dental Unit Waterline Contamination

Effective infection control is one of the cornerstones of good practice and clinical governance. Due to a combination of negative publicity and an increased scientific knowledge of dental unit waterlines’ (DUWL) biofilms and their associated risks, contamination of dental unit waterl ines has become a prominent infection-control issue. The perceived threat to public health from DUWL contamination comes from opportunist ic and respiratory pathogens such as Legionella spp (causative agent o f the pneumonia, legionnaires’ disease), Mycobacteria spp and Pseudomonads. These organisms can be amplified in the biofilm to reach infective concentrations, with the potential for inhalation or direct contamination of surgical wounds.1 During the last five years the American Dental Association (ADA) has specifically targeted DUWL, promoting research and technical developments.2 The ADA recommended to their members that dental unit water should comply with drinking water standards and contain <200 colonies/ml of bacteria (equivalent to that permitted for drinking water). This standard has been adopted by other national dental organisation as being acceptable and achievable. To control contamination of DUWL, the British Dental Association recommends flushing, independent bottled water systems, anti-retraction valves on handpieces, and use of sterile water fo r minor ora l surgery . Denta l equipment manufacturers have in turn responded with a variety of approaches to this complex problem. There are a plethora of automated flushing systems, f i l ters, water disinfectants, independent bottle water systems, and even fully detachable autoclavable DUWL on the market. In the UK, water authority enforcement of European drinking water directives has focused on the prevention of back siphonage from dental surgeries into the mains water supply. Additional safety recommendations can be found in the Health and Safety Commission 2001 Legionnaire’s Disease. The Control of Legionella Bacteria in Water Systems. Approved Code of Practice and Guidance.3 For the first time the code of practice, which applies to all premises covered by the Health and Safety at Work Act 1974, includes dental surgeries. All dentists are required to conduct a statutory risk assessment in their practices. To comply with their legal duties employers must identify and assess sources of risk and prepare a scheme for preventing and controlling the risk. This paper will focus on the relative risk associated with contaminated dental waterlines of respiratory health and the factors that should be taken into account when conducting a risk assessment of DUWL. Detailed analysis of different methods of water decontamination is outside the scope of this paper.