Legionnaires’ disease was first identified and named in 1976 when a group of American Legion conventioneers at the Hotel Bellevue in Philadelphia, PA were taken ill, some fatally, from a contaminated air conditioning system^(1,2). For the majority of people exposed to Legionella bacteria, the outcome is benign. However, for sensitive populations such as newborns, the elderly, those recovering from burns or recent surgery, or those suffering from cancer or chronic lung disease, the outcome can be serious and life threatening⁽³⁾. Immunocompromised patients such as allogeneic and autologous bone marrow transplant recipients, solid organ transplant recipients, and HIV-positive patients are also at high risk for Legionella infection⁽⁴⁾.

Legionella Facts:

• Legionella present one of the most pressing and high-profile problems with respect to waterborne healthcare-associated infections⁽⁵⁾.
• Pediatric hospitals, rehabilitation centers, and long-term care facilities have reported healthcare-associated infections linked to the potable water supply⁽⁴⁾.
• The correct diagnosis of healthcare-associated Legionnaires’ disease is easily overlooked, since it is difficult to distinguish from other forms of pneumonia. Specialized microbiological studies are necessary to detect it⁽⁵⁾.
• Legionnaires’ disease had occurred at two institutions for periods of 12 and 17 years, respectively, before intervention measures were applied. Most of the cases were diagnosed retrospectively, with some only being diagnosed at autopsy^(6,7).
• Contamination of intensive care unit tap water led to a cryptic epidemic of ventilator acquired pneumonia caused by L. anisa⁽⁸⁾.
• The U.S. Centers for Disease Control recently amended their guidelines to stipulate that water in areas housing transplant patients should not contain any Legionella bacteria⁽¹¹⁾.
• In France high risk patients in hospitals must be informed of the danger in using the points of use considered to be at risk (especially showers) when they are not equipped with filters.⁽¹⁵⁾

Challenges to controlling Legionella in healthcare facility systems:

• Legionella are constituents of biofilms that contaminate the internal plumbing of hospital water systems⁽⁴⁾.
• L. pnemophila is amoeba-resistant, meaning that is it able to grow and multiply within an amoeba⁽¹²⁾.
• Studies have confirmed that free-living amoebae are necessary for Legionella multiplication in water biofilms, although they may survive in a latent state in biofilms without amoebae⁽¹³⁾.
• When an amoeba encysts to protect itself from adverse environmental conditions, it may protect L. pneumophila from the effects of chlorine⁽¹²⁾. Recolonization of Legionella is likely to occur long-term after systemic water treatment technologies have been implemented⁽⁴⁾.

Legionella and Point-Of-Use Filtration

• Sheffer et al. evaluated the Pall-Aquasafe^TM water filter in a hospital building with chronic Legionella contamination and determined that point-of-use filters completely eliminated Legionella pneumophila⁽⁹⁾.
• Vonberg et al. evaluated the performance of point-of-use tap water filters in three intensive care units. Without filtration, it was shown that over 90% of 32 samples collected were positive for Legionella at concentrations ranging from 1-106 cfu/ml. In contrast, 250 out of 251 samples recovered from taps fitted with filters for seven days failed to recover any Legionella. In the single positive sample, the residual Legionella concentration was only 1 CFU/mL⁽¹⁰⁾.
• Legionella species measure 0.3-0.9 microns wide by 2 microns long⁽¹⁴⁾. They, and the larger amoeba which they inhabit, are easily retained by point-of-use 0.2 micron filters.

Desinfection measures against Legionella

Method	Advantage	Disadvantage
Thermal desinfection (Heating > 70°C)	Efficient bactericidal effect, no chemistry	No biofilm removal -> rapid recontamination, risk of burning, high personnel costs
Continuous circulation of warm water > 60°C minimal temperature: > 55°C	Reduction of planktonic Legionella (Recommended for new buildings)	No effect on cold water system, possibility of heat transfer from hot water to cold water system
UV-radiation	Strong effect on planktonic Legionella, no chemicals	No reduction of biofilm -> rapid recontamination
Chlorine Anodic Oxidation (electrolytic desinfection)	Proven effect on planktonic Legionella, some effect on biofilm	Chemicals, ineffective against Legionella in biofilm and protozoa

"Comments on investigations on the reduction of Legionella", Der Hygieneinspektor 6/2001, Dr. Peter Schindler, German health ministry department of southern Bavaria

References:
1. Stout, J.E. and V.L. Yu. 2003. Hospital-acquired Legionnaires’ disease: new developments. Curr. Opin. Infect. Dis. 16(4): 337-341.
2. Association of Water Technologies. 2003. An update and statement by the Association of Water Technologies. http://www.awt.org/.
3. Angelbeck, J. October 2004. Stopping Legionella and other waterborne pathogens in their tracks – a global perspective. Water Cond. And Purification. p.62-65.
4. Angelbeck, J.H. 2004. Legionella – a waterborne nosocomial pathogen. Pall Clinical Update.
5. Squier, C., V.L. Yu, and J.E. Stout. 2000. Waterborne nosocomial infections. Curr, Infect. Dis. Reports. 2:490-496.
6. Kool, J.L., D. Bergmire-Sweat, J.C. Butler et al. 1999. Hospital characteristics associated with colonization of water systems by Legionella and risk of nosocomial Legionnaires’ disease: a cohort study of 15 hospitals. Infect. Control Hosp. Epidemiol. 20 798-805.
7. Lepine, L.A., D.B. Jernigan, J.C. Butler et al. 1998. A recurrent outbreak of nosocomial Legionnaires’ disease detected by urinary antigen testing: evidence for long-term colonization of a hospital plumbing system. Infect. Control Hosp. Epidemiol. 19 905-910.
8. La Scola, B., I. Boyadjiev, G. Greub, A. Khemis, C. Martin, and D. Raoult. 2003. Amoeba-resising bacteria and ventilator –associated pneumonia. Emerg. Infect. Dis. 9:815-821.
9. Sheffer, P., J. Stout, R. Muder, and M. Wagener. 2004. New point-of-use water filters to prevent exposure to Legionella and waterborne bacteria. Annual Meeting – Association for Professionals in Infection Control and Epidemiology (APIC), Phoenix, AZ. Abstract #21793.
10. Vonberg, R.P., J. Bruderick, and P. Gastmeier. 2004. Use of terminal tap water filter systems for nosocomial legionellosis prevention. Annual Meeting - The Society for Healthcare Epidemiology of America (Philadelphia, PA). Abstract 191.
11. Sehulster, L., and Chinn, R.Y.W. 2003. Guidelines for environmental control in health-care facilities. MMWR. 2003. 52(RR10):1-42.
12. Greub, G. and D. Raoult. 2004. Microorganisms resistant to free-living amoebae. Clin. Micro. Reviews 17(2):413-433.
13. Murga, R., T.S. Forster, E. Brown, J.M. Pruckler, B.S. Fields, and R.M. Donlan. 2001. Role of biofilms in the survival of Legionella pneumophila in a model potable-water system. Microbiology 147:3121-3126.
14. Stout, J.E., J.D. Rihs, and V.L. Yu. 2003. Legionella. p.809. In (ed.) Baron, E.J., J.H. Jorgensen, M.A. Pfaller, and R.H. Yolken. Manual of Clinical Microbiology, 8th ed. ASM Press, Washington, D.C.
15. Circular Letter DGS/SD7A/SDSC-DHOS/E4 n° 2002/243, published on April 22, 2002.