Control of Legionella Contamination and Risk of Corrosion in Hospital Water Networks following Various Disinfection Procedures

Abstract

bPhysical and chemical disinfection methods have been proposed with the aim of controlling Legionella water contamination. To date, the most effective procedures for reducing bacterial contamination have not yet been defined. The aim of this study was to assess the long-term effectiveness of various disinfection procedures in order to reduce both culturable and nonculturable (NC) legionellae in different hospital water networks treated with heat, chlorine dioxide, monochloramine, and hydrogen peroxide. The temperature levels and biocide concentrations that proved to give reliable results were analyzed. In order to study the possible effects on the water pipes, we verified the extent of corrosion on experimental coupons after applying each method for 6 months. The percentage of positive points was at its lowest after treatment with monochloramine, followed by chlorine dioxide, hydrogen peroxide, and hyperthermia. Different selections of Legionella spp. were observed, as networks treated with chlorinebased disinfectants were contaminated mainly by Legionella pneumophila serogroup 1, hyperthermia was associated with serogroups 2 to 14, and hydrogen peroxide treatment was associated mainly with non-pneumophila species. NC cells were detected only in heat-treated waters, and also when the temperature was approximately 60°C. The corrosion rates of the coupons were within a satisfactory limit for water networks, but the morphologies differed. We confirm here that chemical disinfection controls Legionella colonization more effectively than hyperthermia does. Monochloramine was the most effective treatment, while hydrogen peroxide may be a promising alternative to chlorine-based disinfectants due to its ability to select for other, less virulent or nonpathogenic species.

Ten questions concerning the aerosolization and transmission of Legionella in the built environment

“…Because of naturally occurring fluctuations in numbers, 120 impact of various control methods, 121 and sporadic changes in bulk water concentrations due to periodic biofilm detachment, 122 determining a typical level of Legionella for a given environment is difficult. This issue is exacerbated by a lack of in-depth monitoring studies implementing multiple quantification methods.…”

The Effect of Hydrogen Peroxide on Reducing the Colonization of <em>Legionella spp.</em> in a Hospital Water Network

“…This characteristic trend, with a first stage of L. pneumophila reduction followed by its substitution by less pathogenic Legionella, and a long-term efficacy in reduction of all Legionella species, was highlighted by Marchesi et al [35], applying HP disinfection associated with peracetic acid.…”

“…Initially, Legionella counts were rapidly reduced, remaining stably at lower levels in the first seven months, until complete disappearing of bacteria in more than 90% of samples during the subsequent eighth month. During the treatment, another interesting evidence was the L. pneumophila (serogroups 1, 6, 9) progressive substitution, with environmental species of Legionella, such as L. jamestowniensis [35].…”

Water Hygiene Audit and Legionella Control in Hospitals

“…A range of physical and chemical disinfection methods have been proposed, but up until now, the most effective procedures for controlling contamination have not been defined [20,21]. As was described before, in order to eliminate legionella bacteria, thermal disinfection (heat treatment or heat shock) of hot water is usually recommended.…”