Legionella pneumophila contamination of a dental unit water line system in a dental teaching centre

:  Objective:  This study aimed to evaluate the extent of Legionella pneumophila contamination in a dental unit water line (DUWL) at a Dental Teaching Centre in Jordan. Methods:  Ten dental units were sampled from each teaching clinic, namely conservative dentistry, periodontology and prosthodontics. Samples were collected from the air/water syringe, high-speed hand piece and water cup filler. Sampling time was at the beginning of the working day (before the dental unit was used), after 2 min of flushing, and at midday. Results: Legionella pneumophila counts ranged between 0 and 8.35 × 103 (CFU ml−1). Legionella pneumophila was detected in 86.7% of the dental units at the beginning of the working day, 40% after 2 min flushing and 53.3% at midday. The highest L. pneumophila counts were found at the beginning of the working day which were reduced by flushing the waterlines. The conservative dentistry clinic had the highest contamination level followed by the periodontology and prosthodontics clinics (P < 0.05). The rate of contamination can be ascribed to the dental procedures performed in the clinics, the degree of using the hand pieces, and water softening and heating. Conclusions:  The difficulty of completely eliminating micro-organism contaminating water used for dental treatment and the resulting biofilm suggest that flushing of DUWL can be a first solution in reducing L. pneumophila counts, while the incorporation of a disinfection method is highly recommended. Water heating and softening should be considered in practicing dentistry as factors that may aid in L. pneumophila proliferation inside the DUWL.