Microbial monitoring of water in a dental clinic as a useful tool to device preventive measures

Background Microorganisms found in the water used for dental procedures may represent a considerable health hazard for dental staff and patients, particularly immunocompromised ones. Aim To monitor the microbial contamination of tap water and the dental unit water system (DUWS) in a dental clinic at the University Hospital of Parma, providing a picture of contamination levels, highlighting any variation between different sampling points and sampling times, and providing useful advice on microbial monitoring procedures and preventive measures. Methods Water microbial contamination was assessed during the five working days for one week per month, over a three month period. Tap water and DUWS were sampled before (T0) and after (T1) clinical activity to determine the Total Viable Count (TVC) at 22°C and 36°C, and the presence of Legionella spp. and P. aeruginosa. Results 80% of samples from tap water and more than 90% from the DUWS exceeded the TVC recommended values (Directive 98/83/EC; CDC, 2003). Microbial contamination decreased significantly during clinical activity. TVC median values (cfu/mL) for tap water decreased from 2,304 to 140 at 22°C and from 1,072 to 114 at 36°C; DUWS values went from 48,400 to 16,800 at 22°C and from 12,430 to 6,150 at 36°C. The most contaminated handpiece was the air-water syringe, with a maximum value of 872,000. Differing levels of contamination were observed among the different days, weeks and months. The day with the highest contamination was Monday, both for tap water and the DUWS. No Legionella spp. nor P. aeruginosa were found in tap water. Legionella spp. was found in one sample and P. aeruginosa in 66.6% of samplesfrom the DUWS. Conclusion In the light of our results a global renovation of the dental clinic is being carried out and a microbial monitoring programme that includes tap water and the DUWS is being planned. Special attention will be devoted to monitorings performed on Mondays, which turned out to be “the worst day”.