220 The effects of various interventions for growth of Legionella in pilot-scale water re-circulation system

Friday, March 19, 2010
Grand Hall (Hyatt Regency Atlanta)
Zhaoyan Zhou, MSc , Zhongshan Hospital of Fudan University, Shanghai, China
Bijie Hu, MD, PHD , Zhongshan Hospital of Fudan University, Shanghai, China
Lili Tao, BM , Zhongshan Hospital of Fudan University, Shanghai, China
Linlin Yu, BM , Zhongshan Hospital of Fudan University, Shanghai, China
Xiaodong Gao, BM , Zhongshan Hospital of Fudan University, Shanghai, China
Background: Water distribution systems which colonized by Legionella spp have been implicated in the majority of nosocomial outbreaks of Legionellosis. More than 70% water distribution systems in healthcare facilities in Shanghai were contaminated by Legionella spp based on our survey.

Objective: In order to evaluate the potential of Legionella growth in water distribution system, we constructed a pilot-scale water re-circulation system that allowed simulation of real-world conditions and compared the efficiency of different disinfection treatments applicable to Legionella control.

Methods: A pilot-scale system consists of four PPR re-circulation loops and dead legs. During the study, each of three loops received continuous application of one of the following disinfection treatments: copper-sliver ionization (0.4/0.04mg/L), chlorine dioxide (0.5 mg/L) and thermal eradication (maintained over 55°C). The fourth loop was used as a control. Culture techniques, confocal laser scanning microscopy after fluorescent in situ hybridization and viability staining with the LIVE/DEAD kit were used for planktonic and biofilm flora monitoring.

Results: Before treatments, the system was highly contaminated with L. pneumophila in water (3.4×103/ml) and biofilm (2.4×104/cm2). In the water and the biofilm of the loops, Chlorine dioxide and thermal eradication were very effective in reducing the microbial flora, including L. pneumophila. Heterotrophic bacteria were still detectable after copper–silver ionization application, the contamination remained significantly higher. Copper–silver did not remove the biofilm. Only chlorine dioxide led to detectable effects in the dead leg. After interrupting the treatments, L. pneumophila quickly recovered their initial levels in all cases.

Conclusions: Chlorine dioxide, applied as a continuous treatment, was identified in this study as the most efficient for controlling L. pneumophila in pilot-scale water re-circulation system. Once a system is colonized by L. pneumophila, eradication of the agent from the environment become very difficulty or is practically impossible.