Evaluation of the Effectiveness of a 4-Months Continuous Injection of a Gas Mixture (CO₂ and Inert Gases) on Legionella Contamination of a Hot Water Distribution System

Maria Anna Coniglio^*

Legionella Reference Laboratory, Department of Medical, Surgical Sciences and Advanced Technologies “G.F. Ingrassia”, University of Catania, Catania, Italy.

DOI: 10.4236/health.2015.77096                

Abstract

Within the biofilm and scales Legionella is less far susceptible to the effects of the most frequently used biocides. The objective of this study was to evaluate the effect of a 4-months continuous injection of a gas mixture (CO₂ and inert gas) in the hot water distribution system of a large hotel colonized by L. pneumophila sg3 on limiting biofilm formation and scales and in turn Legionella growth. Before the continuous injection of the gas mixture, out of the 15 sampling points examined every month 60% were colonized by Legionella (mean concentrations of 10² cfu/L in the boilers and the return loop, and 10⁴ cfu/L in taps and showers). One week after the injection of the gas mixture and daily fluxing of the distal outlets, the level of colonization decreased (<10³ cfu/L). When it was decided to flux all the distal outlets only 1 day per week the mean concentration of Legionella increased again (>10⁴ cfu/L) in all the sampling points. Thus, cleaning of the boilers was performed and distal outlets were again fluxed daily. One week after the level of contamination decreased again (<10² cfu/L). Nonetheless, the colonization was not eliminated and when fluxing of the distal outlets was not performed every day the mean concentrations of Legionella raised up to >10⁴ cfu/L. Results indicate that the gas mixture was able to reduce the level of colonization by Legionella only because associated to the fluxing of the distal outlets.

Keywords

Legionella, Gas Mixture, Fluxing, Water Distribution Systems

Conflicts of Interest

The authors declare no conflicts of interest.

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