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Influence of temperature and chemical decontamination on the prevalence of Legionella pneumophila in hot water

Abstract number: P1203

Colombo C., Senn G., Bürgel A., Ruef C.

Objectives: To demonstrate the impact of water temperature and chemical decontamination on prevalence and concentration of Legionella pneumophila (L.p.) in hot water of high risk medical wards (oncology, radiation therapy, organ transplantation units and burn ICU).

Methods: Measurement of L. pneumophila concentration and temperature of hot water of patient care units of the University Hospital of Zurich monthly during the baseline period (A; 2008/2009), a preparatory period with reduced water temperature (B; February – June 2010), the phase prior to chemical decontamination (C; July – September 2010). Chemical decontamination with copper-silver and chlorine dioxide was started in separate hospital areas in October 2010 (period C). Concentrations of chemicals used were measured regularly.

Results: The proportion of positive peripheral sites as well as the concentration of L.p. increased significantly during period B (table), parallel to a significant reduction of the median temperature (p < 0.001). Serotype 1 was the predominant strain. After raising the temperature of the outlets to a median of 62 (period C), respectively 60°C during period D, the rate of positive samples as well as the concentration of L.p. dropped significantly (p < 0.001). Following the introduction of chemical decontamination in October 2010, only one sample was positive for L.p. This sample was found in a unit with copper-silver ionisation. The median residual concentration on peripheral outlets of silver and copper (samples n = 54) was 5.5 mg/l and 108 mg/l respectively. The median residual concentration on peripheral outlets of chlorine dioxide (samples n = 29) was 0.02 mg/l. Between October and December 2010 we noted a significant decrease of mean (7.7 to 2.9 mg/l) and median (7.7 to 2.75 mg/l) concentration of silver (p < 0.001), but not of copper or chlorine dioxide. All measured concentrations were below the upper threshold concentration required for safety of potable water.

Conclusion: Our data show a strong correlation between low water temperature and the appearance of L. pneumophila as well as the positive effect of adequate water temperature (55°C) and the application of chemical decontamination on the prevalence and concentration of L. pneumophila in a hospital hot water system. Chemical decontamination enhances the effect of an increase in water temperature on the reduction of Legionella concentration. Further follow-up is needed to determine the long term effect of these measures.

Session Details

Date: 07/05/2011
Time: 00:00-00:00
Session name: Abstracts of 21st ECCMID / 27th ICC
Subject:
Location: Milan, Italy, 7 - 10 May 2011
Presentation type:
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