Prevention and Control of Legionella Pneumophila at The Toronto Hospital
Although water is the major reservoir of Legionella species it may occasionally be found in other sourced such as soil. Legionella are generally present in very low concentrations, however under certain conditions the numbers of bacteria may increase markedly. Factors known to enhance growth and colonization of Legionella in the environment include water temperature of 25-42ºC, scale and sediments, stagnation and the presence of Amoebae that are capable of supporting growth of Legionella.
Transmission
The primary mode of transmission of legionellosis is inhalation of aerosolized droplets of Legionella organisms. Aerosolization of contaminated warm water via shower heads or tap water faucets can also transmit legionellosis. There is no evidence of person to person transmission. The risk of illness following exposure to legionella may be influenced by the presence or concentration of organisms, the susceptibility of the host, and the virulence properties of the contamination strain.
Basic Preventive Action
(Laboratory monitoring of the hospital environment not required)
1. Monitor the incidence of pneumonia in patients at increased risk of developing the disease. Persons with severe immunosuppression or chronic underlying illnesses, such as hematologic malignancy or end stage renal disease are at markedly increased risk of legionellosis.
2. Hot water-tank discharge temperatures should be maintained at 60ºC. Tanks should be drained or cleaned to remove sediment and scale on a regular basis.
3. Cooling towers, humidifiers, floor drains, and other stagnant water sourced should be inspected, cleaned and disinfected using a specific biocided according to protocols established by the water treatment specialist.
4. Ventilation intakes should be checked to ensure proper sealing of filters. The physical relationship of ventilation intakes to cooling tower should be observed.
5. Other Preventive measures
a. Sterile water should be used in all aspects of administering respiratory therapy (avoid tap water).
b. A schedule must be developed for removing cleaning and descaling of shower heads.
Action to be taken in the event of an outbreak
In the event of an increase in the incidence of hospital acquired legionella pneumonia (1-3 cases identified over a period of up to several months) The Infection Control Committee should convene to:
1. determine that an outbreak exists;
2. review the basic preventive action program;
3. develop a protocol for microbiological investigation of cases;
4. Investigate environmental sources to determine the possible cause of the outbreak.
5. Obtain the advice of the following:
a. The Medical Officer of Health for Metropolitan Toronto (cases are required to be reported to the Medical Officer of Health)
b. The Medical Bacteriologist, Chief of the Reference Laboratory for Legionella Testing, Central Public Health Laboratory Ontario Ministry of Health, regarding clinical specimens.
c. The Chief of Environmental Bacteriology Section, Central Public Health Laboratory regarding appropriate environmental specimens for testing.
Additional measures including hyperchlorination or superheating of the water supply may be necessary if the above interventions are not effective in the control of the outbreak. Details are in the Infection Control Manual Policy number 60:10.
REFERENCES
1) Goetz G., Yu V.L. Screening for nosocomial legionellosis by culture of the water supply and targeting of high-risk patients for specialized laboratory testing. AJIC 1991;19:63-65.
2) Breiman R.F. Modes of transmission in epidemic and non-epidemic Legionella infection: Directions for further study. ASM 1993;30-35.
3) Centres for Disease Control and Prevention. Guideline for prevention of nonsocomial pneumonia. AJIC 1994;22:247-92.
4) Disease Control & Epidemiology Service Public Health Branch, Laboratory Services Branch. Recommendations for control of Legionellae in hospitals. Feb. 1986.
Back to Newsletters Directory
