Abstract
The study aimed to assess the prevalence of Legionella spp. in dental unit waterlines of a dental clinic and to verify whether the microbiological parameters used as indicators of water quality were correlated with Legionella contamination. A risk management plan was subsequently implemented in the dental health care setting, in order to verify whether the adopted disinfection protocols were effective in preventing Legionella colonization. The water delivered from syringes and turbines of 63 dental units operating in a dental clinic, was monitored for counts of the heterotrophic bacteria P. aeruginosa and Legionella spp. (22 °C and 37 °C). At baseline, output water from dental units continuously treated with disinfection products was more compliant with the recommended standards than untreated and periodically treated water. However, continuous disinfection was still not able to prevent contamination by Legionella and P. aeruginosa. Legionella was isolated from 36.4%, 24.3% and 53.3% of samples from untreated, periodically and continuously treated waterlines, respectively. The standard microbiological parameters used as indicators of water quality proved to be unreliable as predictors of the presence of Legionella, whose source was identified as the tap water used to supply the dental units. The adoption of control measures, including the use of deionized water in supplying the dental unit waterlines and the application of a combined protocol of continuous and periodic disinfection, with different active products for the different devices, resulted in good control of Legionella contamination. The efficacy of the measures adopted was mainly linked to the strict adherence to the planned protocols, which placed particular stress on staff training and ongoing environmental monitoring.
Highlights
Legionella spp. are waterborne pathogen bacteria that are frequently isolated from man-made aquatic environments such as hot water plants, shower heads, cooling towers, spas, whirlpools, humidifiers and evaporative condensers
P. aeruginosa and Legionella spp. were detected respectively in 22.2% and 34.9% of the samples (L. pneumophila SG1: 25.4%, L. anisa: 9.5%), the results varied depending on the type of disinfection treatment adopted (Table 4)
In 50% of sample treated with Calbenium®, all collected from the first floor of the main building. Of those treated with Calbenium®, three out of four were contaminated by P. aeruginosa with counts up to 103 cfu/100 mL, much lower than the values considered to be the infective dose in healthy people (>1.5 × 106 cfu/mL) [19]. These results show that the continuous introduction of disinfection products, necessarily used at low levels to minimize their potential toxic effect, was more effective in maintaining the heterotrophic bacterial counts within the recommended standards in output water of dental devices, while this treatment was not always able to control microorganisms such as Legionella and P. aeruginosa, which are very resistant to disinfectant treatments both on account of their intrinsic characteristics and because they are protected within the biofilm [41]
Summary
Legionella spp. are waterborne pathogen bacteria that are frequently isolated from man-made aquatic environments such as hot water plants, shower heads, cooling towers, spas, whirlpools, humidifiers and evaporative condensers. Legionellae may colonize dental unit waterlines, i.e. the narrow-bore plastic tubing that carries water to the high-speed handpieces and air/water syringes of dental chairs. The output water from dental units may be a potential source of infection for both dental health care personnel and patients. Legionella is frequently detected in the output water of dental devices [7,8,9,10,11,12,13]. Isolation of Legionella is frequently reported, where there are multiple chairs (e.g., dental schools), only a small number of case-reports of Legionella infection directly linked to contaminated dental waterlines have been described. A fatal case of pneumonia due to Legionella was reported in an
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