46- Legionelle pneumophilia and chlorine dioxide

 

https://www.researchgate.net/publication/5412611_Molecular_epidemiology_of_Legionella_pneumophila_serogroup_1_isolates_following_long-term_chlorine_dioxide_treatment_in_a_university_hospital_water_system

Molecular epidemiology of Legionella pneumophila serogroup 1 isolates following longterm chlorine dioxide treatment in a university hospital water system

B. Casina,*, P. Valentinia, A. Baggiania, F. Torraccaa, S. Frateschib,L. Ceccherini Nellib, G. Privitera Unit of Hospital Hygiene and Epidemiology, Azienda Ospedaliera eUniversitaria Pisana, Pisa, Italy Department of Experimental Pathology, University of Pisa, Pisa, Italy Received 10 July 2007; accepted 6 March 2008 Available online 24 April 2008

 

 Abstract:

This paper describes the results of a five-year monitoring programme applied to the water distribution system of the University Hospital of Pisa (Italy). The purpose of the programme was to evaluate the efficacy of an integrated water safety plan in controlling Legionella spp. colonisation of the potable water system. The impact of the safety plan on the ecology of legionella in the water network was evaluated by studying the genetic variability and the chlorine susceptibility of the strains isolated prior to, and throughout, the application of continuous chlorine dioxide treatment. After 45 months of water hyperchlorination, Legionella spp. were still present but the positive supply points were reduced by 79.4%. The samples exceeding 10(3)cfu/L were reduced by 83.8% and the mean counts showed a decrease of 94.6%. The majority of the isolates belonged to Legionella pneumophila serogroup 1 (overall positivity rate: 161/423; 38%). Molecular typing was performed on 61 isolates (37.9% of the positive samples) selected on spatial and temporal criteria. This revealed the circulation and the persistence in the hospital environment of three prevalent types of L. pneumophila Wadsworth, demonstrating allelic and electrophoretic characteristic profiles and different chlorine susceptibility. Two of these, one predominant and pre-dating the sanitation regimen, and one other isolated after three years of water treatment, were chlorine tolerant. Despite the ineffectiveness of chlorine dioxide in eradicating L. pneumophila, the risk management plan adopted appeared to discourage further cases of nosocomial legionellosis.

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Chlorine dioxide is usually considered a moreeffective disinfectant than chlorine on a mass-dose basis. However, in water at pH 7, freeresidual chlorine in the form of hypochlorous acidis somewhat more effective than chlorine dioxide,so that the rate of legionella inactivation by thetwo chemical oxidants, chlorine or chlorine di-oxide, is similar in our experimental condi-tions.22,23We believe therefore that the chlorinesusceptibility test performed is a good proxy ofthe effect of chlorine dioxide on Legionella spp.Following these observations, our hospital wa-ter safety plan, relying on chlorine dioxide forsanitation, has been modified to include point-of-usefiltration as an additional measure in selectedwards, such as transplant, haematology, oncologyand intensive care units. The application of filtersto terminal point of use may appear to beexpensive, but may be cost-effective when com-pared with other interventions that involve com-plex installation and/or high operating costs, suchas increasing water temperature to 60 C. Thiswould require the application of thermostatic de-vices at each tap. Point-of-use filtration as an ad-junct to chlorine dioxide treatment offers someadvantages; installation can be limited to selectedtaps in high-risk areas and maintenance is simple.Moreover filters with an operating lifespan of onemonth have been recently developed, reducing op-erating costs.24e26146 B. Casini et al.

In conclusion, the typing methods used helpedto analyse the spread of Legionella spp. in the wa-ter distribution system of the hospital and allowedconfirmation that chlorine-tolerant clones can per-sist despite chlorine dioxide treatment. Standardenvironmental surveillance methods, based onlyon qualitative and quantitative culture of Legion-ella spp., and technical assessment of the watersystem, may not be sufficient to determine themost effective and efficient disinfection method,and should, at least in some instances, be accom-panied by in-vitro evaluation of the susceptibilityof the environmental isolates to sanitising agents

 

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