Comparison of the efficacies of disinfectants to control microbial contamination in dental unit water systems in general dental practices across the European union

Dental unit water systems (DUWS) are used to irrigate the oral cavity during dental treatment. Water delivered from these devices is not sterile and has been shown to contain high numbers of bacteria (9, 38, 52). Biofilms accumulating on the inner surface of the tubing can be responsible for high levels of contamination of water delivered by DUWS (21, 38, 51). A number of surveys have reported that the majority of DUWS are supplied by tap water (54). European Union (EU) guidelines recommend that tap water should be delivered at <100 CFU · ml−1 (2); however, once the water enters the DUWS the number of bacteria can increase, with numbers as high as 1.6 × 108 CFU · ml−1 having been recovered in the outflow (12). Such high numbers can result from numerous factors, including ambient temperatures, stagnation, and the presence of biofilm (30). In the United States, the American Dental Association (ADA) and the Centers for Disease Control and Prevention have proposed a guideline for DUWS water of ≤200 CFU · ml−1 (equivalent to that required for dialysis water) (1). Currently, dentists across the world have little or no evidence-based guidelines to control bacterial numbers in DUWS. Typically, patients in the EU visit general dental practices (GDPs) every 6 months, with over 20 million visits per year in 1998 in one large EU country alone (5). During almost every visit, the patient and the dental health care staff are exposed to the water from DUWS. These medical devices have the potential to harbor opportunistic or frank pathogens, and Legionella pneumophila, Mycobacterium spp., Pseudomonas aeruginosa, and Candida spp. have been recovered from DUWS (4, 7, 28, 34, 46, 56). Exposure of dental personnel to such pathogens can be inferred from the finding that dentists have significantly higher antibody titers to L. pneumophila than individuals in other, equivalent employment sectors (10, 11, 24, 35), and asthma may be associated with occupational exposure to endotoxin in aerosols from contaminated DUWS (29). In addition, P. aeruginosa isolated from a DUWS was found to be responsible for the hospitalization of two patients following a visit to a dental surgery (19). The presence of pathogens has further implications when one considers that failure of the three-in-one hand piece antiretraction valve (32, 37) could result in microorganisms being transferred among patients (cross-infection). A wide range of disinfectant products are now being developed for use in DUWS, and these have been evaluated using a variety of approaches (39, 48, 49), although rarely have these products been compared in a general dental practice setting. The aim of this study was therefore to evaluate and compare the levels of control achievable by the application of different disinfectants to DUWS in GDPs.