Comparison of the ActiDes-Blue and CARELA HYDRO-DES technology for the sanitation of contaminated cooling water systems in dental units

Background: The hygienic-microbiological control of 6 dental units being in use for the past 16 years revealed a significantly increased microbial contamination of their cooling water system. In order to comply with the requirements of the drinking water directive (“Trinkwasserverordnung”), the commercially available production system ActiDes, producing on-site ActiDes-Blue which is based on hypochlorous acid (HOCl) and generated by anodic oxidation, was investigated. Method: Water samples from the 6 contaminated dental units were examined for the total number of colony forming units (cfu), contamination with molds, L. pneumophila and P. aeruginosa. The control period for the total colony count was 4 weeks (8 samples/unit). The subsequent application phase of the ActiDes-Blue procedure was 6 months (31 samples/unit). Additionally, the redox potential and the pH value were measured. Futhermore, the decontamination agent CARELA HYDRO-DES, a two component agent based on H2O2 with the addition of a mixture of sodium hydrogen sulphate and sulphuric acid in an aqueous solution effective at 0.1% and higher, was applied in a unit that had been put out of service for a month before. Before application, the system was first filled with a 5% solution of the alkaline pre-cleaning agent CARELA Solvent for bacterial slime; the system was left with this solution for 1 h. The pre-cleaning agent was then completely displaced from the system with tap water and a decontaminating solution of 5% CARELA HYDRO-DES and left in place for 1 h. Results: Drinking water quality level was reached only twice during the control phase. The average values of the dental units ranged between 3,633 CFU/ml and 29,417 c/ml. During the application phase, drinking water level could be achieved in 11 water samples. In another 6 water samples a total colony count of <150 cfu/ml was reached. The average values for the dental units' total colony count ranged between 529 cfu/ml and 87,450 cfu/ml. No significant differences between the control phase and the action phase could be demonstrated. During the control phase, contamination of the water samples with a mold was noticed so that examinations for molds were carried out beyond the scope of the drinking water directive. For this parameter as well, no significant differences between the phases of the study could be shown. The Legionella load of the dental units was low. L. pneumophila were yielded in only 4 out of 130 water samples. During the control phase, twice colony counts at 50 cfu/1,000 ml and 110 cfu/1,000 ml were measured. During the action