207 Introduction Patients and staff of dental clinics are frequently at risk for infections. They are regularly exposed to water from aerosols generated during work, therefore the quality of dental unit water is of great importance, and Dental Unit Water Line (DUWL) contamination has become alarm- ing [1]. The presence of opportunistic and pathogenic bacteria, such as Staphylococcus aureus, Pseudomonas aeruginosa and Legionella pneumophila in dental units water has been reported in several studies [2-7]. The presence of bacterial biofilms on the inside of DU- WLs has been well documented and recognized as an undisputed source of contamination for water used in pa- tient dental treatment [8, 9]. The risk of acquiring infec- tions through Dental Unit Water Systems (DUWS) sup- plies is known to be not very uncommon. Often potential pathogenesis can spread through surgical procedures, lo- cal mucosal contact, ingestion and inhalation [10]. In particular, aerosols containing biological material (sa- liva, blood, and dental plaque) and microorganisms are produced by high-velocity rotating instruments and air- water sprays or ultrasonic scalers [11, 12]. Splatter and aerosols from dental procedures may infect health care personnel [13]. Smaller particles (<5 µm) can float in the air and have the potential to penetrate in the small passages of the lungs, while larger ones settle easily onto environmental surfaces which can become contaminated during patient care [12, 14-18]. Certain surfaces, especially clinical contact surfaces that are frequently touched (e.g. dental unit switches, light handles, drawer knobs), can act as reservoirs of microor- ganisms. When these surfaces are touched, microorgan- isms can be transferred to instruments, other environ- mental surfaces, or to the nose, mouth or eyes of health- care workers or patients [19]. Despite everything, data on microbial contamina- tion in the dental clinic environment are not exhaus- tive [11, 12, 15, 16, 18-26]. Moreover, while the evaluation of water contamina- tion is based on generally accepted and standardized sampling and processing protocols and well defined threshold values [27, 28], methods for air and surface sampling are still debated [28, 29] and no recommend- ed levels of contamination for dental clinics have been established. Since its founding, the working group “Hygiene in Den- tistry” of the Italian Society of Hygiene, Preventive Medicine and Public Health (S.It.I.) analyzes the aspects ORIGINAL ARTICLE Environmental microbial contamination in dental setting: a local experience M. GUIDA, F. GALLÉ * , V. DI ONOFRIO * , R.A. NASTRO, M. BATTISTA ** , R. LIGUORI * , F. BATTISTA ** , G. LIGUORI * Department of Structural and Functional Biology, University of Naples “Federico II”; *  Chair of Hygiene and Epidemiology, Department of Studies of Institutions and Territorial Systems, University of Naples “Parthenope”; **  Complex Operating Unit of Odontostomatology and Maxillo-Facial Surgery, Pellegrini Hospital, Naples, Italy Key words Microbial contamination • Dental clinic • Environmental microbiological monitoring Summary Introduction. Patients and operators are exposed during dental practice to an infective risk, which derives especially from micro- organisms suspended in aerosols. Environmental microbiologi- cal monitoring in dental settings represents a good instrument to detect critical situations. Methods. In order to investigate environmental microbial contami- nation level in a local reality, we analyzed water, air and surfaces samples of a community-based dental facility by using protocol and threshold values proposed in a recent multicenter study carried out by the Italian Society of Hygiene, Preventive Medicine and Public Health (S.It.I.) working group “Hygiene in Dentistry”. Microbial contamination was assessed in the same room for 4 non-consecu- tive weeks during all the five working days, before and at the end of the daily activity. Air was sampled also during clinical activity, through both active and passive sampling systems. Results. Contamination of water showed a decrease during activ- ities, while a decrease in air contamination was registered only at the end of the day. Passive sampling values resulted more often above threshold values adopted. At the same time, surfaces con- tamination increases at the end of the activity. It seems that in the dental clinic analyzed microbial buildup represents the higher critical element. No differences have been registered among the different days of the week. Discussion. Our study highlights the need to improve disinfection procedures and air treatment systems in the considered environ- ment. Microbiological monitoring could represent an important element to detect the presence of risk factors and to adopt control measures. The full article is free available on www.jpmh.org J PREV MED HYG 2012; 53: 207-212