Microbial risk assessment of dental unit water systems in general dental practice in Greece A. Mavridou, J. Kamma, G. Mandilara, P. Delaportas and F. Komioti Technological Educational Institution of Athens, Ag Spyridona, 12210 Aigaleo, Greece (E-mail: amavridou@teiath.gr) Abstract Water was sampled from source water, the 3-in-1 syringe and the air rotor water line of dental unit water systems (DUWS) in general dental practice in Attica, Greece. A section of the water line supplying the 3-in-1 syringe was cut for biofilm analysis. High total viable counts, Mycobacterium spp. and Pseudomonas aeruginosa were detected in the samples. Back siphonage was evidenced by the presence of blood and the recovery of oral anaerobes from the samples. Legionella pneumophila was recovered from 16.1% of biofilm samples. All tested disinfectants reduced the total viable counts of the DUWS to ,100 CFU/mL. Keywords Dental unit water system; disinfectants; Greece; pathogens; risk assessment Introduction The water in dental unit water systems (DUWS) may originate from a variety of sources including potable tap water or mineral water. The water delivered from these devices has been shown to contain high numbers of bacteria (Blake, 1963; Williams et al., 1995b; Smith et al., 1999; Singh et al., 2003). In the USA, the American Dental Association (ADA) and the Center for Disease Control and Prevention (CDC) have recommended a standard of 200CFU/mL (equivalent to that required for dialysis water). The EU has yet to set an equivalent standard for DUWS. Nevertheless, the new EC Directive for the quality of potable water (98/83/EC) indicates that colony counts at 22 8C should not present an indicative change. However, once the water enters DUWS the number of bacteria can increase as a result of various factors including ambient temperature, stagnation and the presence of biofilms (Pankhurst et al.,1998). Biofilms accumulating on the inner surface of the tubing are responsible for high levels of contamination on DUWS (Williams et al., 1995a). Opportunistic pathogens (such as Legionella pneumophila, Mycobacterium spp., Pseudomonas aeruginosa and Candida spp.) have been recovered from DUWS (Atlas et al., 1995). Such pathogens may pose a risk especially to immunocompromised patients. Furthermore, the carriage of pathogens by asymptomatic patients has implications for cross-infections, as water-line and hand-piece anti-retraction valves can malfunction (Walker et al., 2004). Pseudomonas aeruginosa has been transmitted to a patient through a dental practice (Pederson et al., 2002). Failure of the 3-in-1 hand piece anti-retraction valve can cause further problems, even leading to the detection of blood in the water (Porter, 2002). Exposure of dental personnel has been implied since dentists have a significantly higher antibody titre to L. pneumophila than other equivalent employment sectors (Atlas et al., 1995, Challacombe and Fernandes, 1995). A wide range of disinfec- tants on the market promise to improve the quality of water in dental units and some of them have been evaluated (Walker et al., 2001). The aims of this study were: (1) to assess the microbiology of DUWS in general den- tal practices in Attica, Greece; and (2) to evaluate and compare the efficacy of a variety Water Science & Technology Vol 54 No 3 pp 269–273 Q IWA Publishing 2006 269 doi: 10.2166/wst.2006.479 Downloaded from https://iwaponline.com/wst/article-pdf/54/3/269/431742/269.pdf by guest on 17 November 2018