Dental Unit Water Lines (DUWLs) and Legionella Management
Majority of dental equipment is powered by compressed air.
The compressed air also drives water to equipment.
The water supply to the chairs is usually from bottled water; ideally sterile, but more usually distilled or RO water is used. Infrequently direct mains water is used, although there may be a mains supply that can be used in case the bottled supply runs empty (subject to category 5 back flow prevention Type A air gap)
In accordance to Department of Health Guide for Decontamination in primary care dental practices (HTM01-05) published in March 2013 the water used to supply dental unit water lines (DUWLs) must comply with drinking water standards and bacteria level should not exceed 100 to 200 cfu/ml (HTM01-05 Paragraph 6.79).
No currently available single method or device will completely eliminate bio-contamination of DUWLs or exclude the risk of cross-contamination with harmful bacteria (e.g. Pseudomonas Aeruginosa, Legionella species, non-tuberculous mycobacteria).
HTM01-05 Recommended control regime:
Self-contained water bottles (bottled water system) should be removed, flushed with distilled or RO water and left open to the air for drying overnight. They should be stored inverted. (Paragraph 6.83)
Where visual contamination is present, flushing with a suitable disinfectant followed by thorough washing is necessary. The manufacturer’s instructions will specify the disinfectant to be used and may also require the continuous presence of antimicrobial agents to prevent the build-up of biofilms. (Paragraph 6.84)
DUWLs should be flushed for at least two minutes at the beginning and end of the day and after any significant period when they have not been used (for example, after lunch breaks). In addition, they should also be flushed for at least 20–30 seconds between patients. (Paragraph 6.85)
In accordance to HTM01-05 disinfection of dental unit water lines (DUWLs) should be carried out periodically (we recommend minimum once per week).
A typical approach will be to clean and disinfect the whole system using a disinfectant approved by the dental unit manufacturer, to remove biofilms from the system components. Cleaning should be followed by the regular flushing and disinfection of system components, pipework and bottles on a twice daily basis – typically at the start and finish of each working day – in order to maintain the system as free from biofilm. Blends of disinfectants are available for this purpose in this type of equipment.
Although some manufactures claim that using their product negates the need for removing water bottles on a daily basis. If water is left overnight with disinfectant, this should be shown to work by the testing of bacterial levels (TVC’s). Testing should be carried out using a UKAS accredited laboratory.
While the use of dip-slides test is not advocated by HTM01-05 (Paragraph 19.68) as they are not sensitive enough for use as a test for drinking water quality and detect legionella bacteria, if used correctly, in line with manufacturers instructions, they are capable of detecting the higher levels of bacteria associated with the presence of biofilms.
The frequency of all checks should be led by the risk assessment completed on a regular basis.
As most buildings, dental practices will also have domestic hot and cold water system present. Any water system can become contaminated with legionella bacteria, therefore legionella risk assessment must be carried out to identify the risks associated and implement suitable written scheme of control to eliminate (if possible) or control the risk. The assessment must be carried out by a competent person.
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