What are the key principles of preventing Legionella?

Legionella spp. are strictly waterborne pathogens. Monitoring the hospital water system and prevention of aspiration of contaminated drinking water is the key principle of preventing Legionellosis.

What are the conclusions of clinical trials and meta-analyses regarding control of Legionella?

Hospital construction, choice of materials for water pipes and level of maintenance affect formation of biofilms and contamination with Legionella spp.

Monitoring of hospital water and risk assessment should guide the decision for point-of-use filters, physical (heating, ionization) or chemical (disinfection) prevention measures.

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What are the consequences of ignoring the control of Legionella?

High levels of water contamination with Legionella spp. propagate severe nosocomial pneumonia in individual highly susceptible patients and are a risk for hospital wide outbreaks of Legionnaires´ disease.

What other information supports Legionella research, e.g., case-control studies and case series?

Hospital-acquired outbreaks of legionellosis have been reported worldwide as have case series for specific i.e. immunocompromides patient populations. Clonal identity of water and clinical isolates was demonstrated in several reports.

Summary of current controversies.

The controversies concentrate on the timing, extent, technique and interpretation of environmental cultures and the best way to decontaminate hospital water systems.

i) Most European countries as well as the US Veterans Healthcare System recommend routine testing of hospital drinking water for the presence of Legionella spp. whereas the US CDC advises testing only after cases of legionellosis have been diagnosed. Routine testing is recommended, however, for transplant centers.

ii) The proportion of water sites colonized with Legionella might be a more valuable predictor for the risk of acquiring legionellosis than the concentration in individual samples.

iii) Technique of probing and microbiological workup of the samples has to follow accepted and standardized protocols to achieve comparable results.

iv) The minimal infectious dose of Legionella is not known, is most likely different in different groups of patients and depends from the predominant legionella species and serotypes. The basic question as to how many Legionella are necessary in the environment to cause infection in humans is still not answered!

v) Several modalities for the hospital water system as well as point of use measures are available.

What is the impact of Legionella and the need for control relative to infections at other sites or from other specific pathogens?

More than two thirds of legionellosis are community-acquired. Nosocomial cases are either part of an outbreak or have a high mortality risk in sporadic cases most likely in immunocompromised patients.

Overview of important clinical trials, meta-analyses, case control studies, case series, and individual case reports related to infection control and Legionella.

See Table I for a summary of relevant research.

Table I.
Recommendation Timing of Environmental Sampling Action
WHO [2007] Sampling according to individual risk assessment: Water Safety Plan Define target and alert levels for risk populations
CDC [2003]All health care facilities No recommendation for routine culturing If ³ 1 case of nosocomial legionellosis
CDC [2003]Transplantation Units Periodic culturing Aim at undetectable levels of Legionellaspp. in the water systems of units caring for high risk patients
US Veterans Healthcare System [2008] Routine culturing according to algorithm for annual evaluation If ³ 30% of outletstested positive for L.pneumophila SG1
Most European Countries Routine culturing of drinking water High risk patients: Legionella spp. should not be detectableDifferent target levels for standard risk patients in individual countries

Controversies in detail.

See Table II for a summary of the controversies related to Legionella.

Table II.
Measures Methods Comments References
Design, operation and maintenance of hospital water systems Skilled technical staffChoice of pipe materials WHORogers 1994
Temperature control Continuous or intermittent heating of the hot-water system > 50°Ce.g. “superheat and flush”Heating at the point of use (local boilers for the cold water system)


Stress onwater-system, not all parts of the system can be sufficiently heated, boilers have to be replaced regularly

Best 1984Marchesi 2011
UV – Light

No chemicals

May be effective in restricted areas and as an additional method

Franzin 2002
Chemical Disinfection Copper-silver ionization

Regarded by many authors as the most effective long-term disinfection method

Monitoring of ion concentrations and water ph is mandatory

Modol 2007Chen 2008Shih 2010
Chlorine dioxide

Conflicting experiences are reported


Providing an effective concentration in the water system is challenging

Zhang 2007 Hosein 2005
Hyperchlorination Problematic due to lack of efficiency and severe adverse effects Garcia 2008

No long-term experiences

Technically demanding method

Several adverse effects have been reported

Flannery 2006
Point of use filters

Safe, easy to use e.g. in emergency situations

Expensive if used for larger areas

Sheffer 2005

What national and international guidelines exist related to Legionella?

In most countries recommendations regarding Legionella spp. are part of legal regulations for the quality of drinking water. Thus apart from the WHO recommendations, the CDC and European guidelines (ECDC) readers might refer to the national regulations of their country of interest.

What other consensus group statements exist and what do key leaders advise?

Several excellent and comprehensive overviews concerning prevention and control of Legionella have been provided by Lin, Stout and Yu.

The European Working Group for Legionella Infections (EWGLI) offers several guidelines concerning all aspects of management of Legionella spp.



Levin, AS. “Nosocomial legionellosis: prevention and management”. Expert Rev Anti Infect Ther. vol. 7. 2009. pp. 57-68.

Lin, YE, Stout, JE, Yu, VL. “Prevention of hospital-acquired legionellosis”. Curr Opin Infect Dis. vol. 24. 2011. pp. 350-356.

Lin, YE, Stout, JE, Yu, VL. “Controlling Legionella in hospital drinking water: An evidence-based review of disinfection methods”. Infect Control Hosp Epidemiol. vol. 32. 2011. pp. 166-173.

Selected Articles:

Best, M, Goetz, A, Yu, VL. “Heat eradication measures for control of nosocomial Legionnaires´disease: implementation, education, and cost analysis”. Am J Infect Control. vol. 12. 1984. pp. 26-30.

Chen, YS, Lin, YE, Liu, YC. “Efficacy of point-of-entry copper-silver ionisation system in eradicating Legionella pneumophila in a tropical tertiary care hospital:implications for hospitals contaminated with Legionella both in hot and cold water”. J Hosp Infect. vol. 68. 2008. pp. 152-158.

Flannery, B, Gelling, LB, Vugia, DJ. “Reducing Legionella colonization in water systems with monochloramine”. Emerg Infect Dis. vol. 12. 2006. pp. 588-596.

Franzin, L, Cabodi, D, Fantino, C. “Evaluation of the efficacy of ultraviolet irradiation for disinfection of hospital water contaminated by Legionella”. J Hosp Infect. vol. 51. 2002. pp. 269

Garcia, MT, Baladron, B, Gil, V. “Persistence of chlorine-sensitive Lagionella pneumophila in hyperchlorinated installations”. J Appl Microbiol. vol. 105. 2008. pp. 837-847.

Hall, KK, Giannetta, ET, Getchell-White, SI, Durbin, LJ, Farr, BM. “Ultraviolet light disinfection of hospital water for preventing nosocomial Legionella infection: a 13-year follow-up”. Infect Control hosp Epidemiol. vol. 24. 2003. pp. 580-583.

Hosein, IK, Hill, DW, Tan, TY. “Point-of-care controls for nosocomial legionellosis combined with chlorine dioxide potable water decontamination: a two-year survey at a Welsh teaching hospital”. J Hosp Infect. vol. 61. 2005. pp. 100-106.

Marchesi, I, Marchegiano, P, Bargellini, A. “Effectiveness of different methods to control legionella in the water supply: ten-year experience in an Italian university hospital”. J Hosp Infect. vol. 77. 2011. pp. 47-51.

Modol, J, Sabria, M, Reynaga, E. “Hospital-acquired legionnaires disease in a university hospital: impact of the copper-silver ionization system”. Clin Infect Dis. vol. 44. 2007. pp. 263-265.

Rogers, J, Dowsett, AB, Dennis, PJ. “Influence of plumbing materials on biofilm formation and growth of Legionella pneumophila in potable water systems”. Appl Environ Microbiol. vol. 60. 1994. pp. 1842-1851.

Sheffer, PJ, Stout, JE, Wagener, MM, Muder, RR. “Efficacy of new point-of-use water filter for preventing exposure to legionella and waterborne bacteria”. Am J Infect Control. vol. 33. 2005. pp. S20-S25.

Shih, HY, Lin, YE. “Efficacy of copper-silver ionization in controlling biofilm- and plankton-associated waterborne pathogens”. Appl Environ Microbiol. vol. 76. 2010. pp. 2032-2035.

Zhang, Z, McCann, C, Stout, JE. “Safety and efficacy of chlorine dioxide for Legionella control in a hospital water system”. Infect Control Hosp Epidemiol. vol. 28. 2007. pp. 1009-1012.