Update on Legionella

Newsletter ID: Pen #33, 2008.
Services: Environmental Laboratory Services

Legionnaires’ disease was first described in 1976 after an outbreak of fatal pneumonia at an American Legion conference in Philadelphia. The outbreak involved 221 cases of respiratory illness and 34 persons eventually died. The microorganism identified by the Centres for Disease Control and Prevention in 1977 as responsible for this outbreak, was named Legionella pneumophila after the Philadelphia outbreak. The source of the Legionella was the hotel’s cooling tower.

Inhalation of Legionella bacteria can cause two separate respiratory infections, Legionnaires’ disease and Pontiac Fever. Of the two, Legionnaires’ disease is more serious with possible fatalities, particularly with immune compromised persons, the elderly, smokers, etc. The fatality rate is variously reported as 10-20%. Pontiac fever  is a non-fatal flu-like disease of short duration that does not cause pneumonia.

Legionnaires’ disease is caused by inhaling water aerosols (fine water droplets) containing Legionella pneumophila bacteria. Typical sources of Legionella aerosols include drift from cooling towers, shower heads, faucets (particularly faucets with aerators), decorative fountains, water gardens, condensate drip pans, hot tubs and whirlpools.

Legionella bacteria are normal inhabitants of lakes, streams and soils. They prefer warm water above 20˚C and most do not survive at temperatures above 60˚C. Legionella typically do not grow in water temperatures less than 20˚C. The growth of Legionella pneumophila can be found in water temperatures ranges of 20 to 50˚C with the ideal growth range being 35 to 45˚C. The disinfection range is 70 to 80˚C.

Typical Conditions That Promote Legionella Growth

Typical conditions in building water systems that would promote Legionella growth with desirable water temperatures include sediment, dead legs or stagnant water, corrosion, or biofilm. For example:

• Domestic hot water storage tanks with lower water temperatures and sediment build up can promote Legionella growth. The bacteria can be released from the sediment by surges in water pressure and then the bacteria can be aerosolized by faucet aerators, shower heads or other devices.
  
  
• Cooling towers if  improperly maintained can become sites of major Legionella growth. The contaminated drift (water droplets) from a tower can enter the building via outside air intakes, openable windows or travel to adjacent buildings and disperse in open public areas via air currents. 
  
  
• Dead legs or stagnant water can occur in potable water lines feeding fixtures, for example in a hotel room that has not been used for a period of time. This “still” water can amplify bacteria growth which can be aerosolised into the occupied space via shower heads or faucet aerators. In addition, unused water distribution lines in the construction area of an occupied building which are not capped and drained can release contaminated water in the main potable water lines serving the occupied area of the building and cause a risk to occupants.
  
  
• Biofilm (slimy deposits  of bacteria, protozoa, amoebae, etc.) can be found on the metal or wood surface of water sumps  in cooling towers. Biofilm can support and conceal Legionella which can resist standard chemical disinfection. Consequently water agitation could release Legionella which would be introduced into the air via drift from the tower. Analysis of water samples from cooling towers sometimes may not identify Legionella; however swabbing of the biofilm could identify Legionella concealed within the biofilm even if the water samples were negative. 
  
  
• Biofilm concealing Legionella can be trapped within scale or corrosion inside potable piped services. The Legionella can be released into the water by the pressure surges that happen during plumbing renovations or water shutdowns and start up. The Legionella entrapped in biofilm can be resistant to hot water disinfections.

Obligation to Workers 

Exposure to Legionella pneumophila can result in serious consequences. In 2005, a Legionella outbreak in a long term care facility in Scarborough Ontario resulted in a total of 135 infections and 23 fatalities. The source of the Legionella is believed to have been the building’s cooling tower. Following this occurrence, the Ministry of Labour issued “Information Bulletin Workplace Health and Safety Guideline — Legionella”. The bulletin was issued “to remind employers of their obligations to protect the health and safety of workers, provide information about Legionnaires’ disease and re-affirm expectations of employers and workers”. The bulletin states that employers have a general duty under the Occupational Health and Safety Act to take every precaution reasonable for the protection of a worker. This would include maintenance of water systems and ventilation systems in buildings to protect workers from the hazard of Legionella exposure.

Pinchin Services

Physicians or Health Care Facilities Must Report

In Ontario, a physician or health care facility diagnosing a case of Legionella pneumophila must report the condition to the regional health unit. The health unit will work with the health care facility to identify if there is an environmental source of concern, and review remediation actions that might be required. For example a regional health unit, for a Municipality in Ontario, has a protocol that in the event of a outbreak all cooling towers within 1.5 kilometres of a suspect tower shall be sampled for Legionella pneumophila.

ASHRAE Guidelines

ASHRAE Guideline 12 -2000 “Minimizing the risk of Legionellosis Associated with Building Water Systems” and the Cooling Technology Institute “Legionellosis Guideline: Best Practices for Control of Legionella” are often referenced by regulatory agencies during an outbreak. The ASHRAE guideline provides guidance to minimize Legionella contamination in building water systems such as potable water systems, hot tubs, whirlpools, cooling towers, etc. The guideline provides operational advice to minimize the risk of Legionella growth. For example, maintenance staff should periodically flush hot water tanks to prevent the accumulation of sediment and check that the heating elements provide an even water temperature through the vessel to minimize cold spots. The guideline includes a summary of procedures for cleaning and treatment of cooling towers prior to shutdown and start-up. For emergency decontamination, ASHRAE refers to the Cooling Technology Institute guideline which outlines a biocide emergency disinfection procedure. In addition, regular inspection and physical maintenance are crucial. This includes minimizing water stagnation, maintaining good system cleanliness to minimize sediment build up and using high efficiency mist eliminators. Both of these standards emphasise the importance of implementing and maintaining comprehensive preventative maintenance measures to minimize the growth of Legionella pneumophila.

Legionella Prevention Programmes

Pinchin recommends Legionella Prevention Programmes for all buildings with systems at risk of developing Legionella growth, particularly hospitals, long term care facilities, or other buildings serving immune compromised occupants.

Building operators may test water samples for Legionella on a proactive basis to supplement and document the effectiveness of the Legionella prevention measures. Water testing could be used for the following purposes. ⁱ

• Verify the effectiveness of the  water treatment protocol  and mechanical  decontamination procedures;
• Assist in tracing  an outbreak source; and
• Proactively monitor water quality in high risk facilities such as health care centres.

However sampling by itself does not negate the necessity of an effective well documented preventative maintenance program. It is important that the testing laboratory be selected with care and that the field technicians follow well documented sampling procedures and strategies, particularly where there is a litigation risk. The culturing method for Legionella detection continues to be the most recognized or “Gold Standard” method.

The laboratory should have a documented Standard Operating Procedure using recognized methods and be able to prepare culture isolates to identify the Legionella species (i.e. pneumophila, provide a count of total Colony Forming Units (CFU’s) and identify serotypes and CFU’s of each serotype. Samples should be delivered to the laboratory within 24 hours. Consequently, selection of a local or provincial laboratory is recommended as water samples can sometimes be delayed by customs during cross border deliveries.

Effective and Experienced  Interpretation of Results is Necessary 

Effective and experienced  interpretation of sample results is necessary to evaluate occupant risk. The US Occupational Safety and Health Association have published the following guidelinesⁱⁱ for the interpretation of Legionella water samples: 

   
OSHA does state that these guidelines are intended for water systems being used by healthy individuals and are not necessarily protective of immune compromised persons. Therefore, in a health care facility, Infection Control should be informed of any positive results. In addition OSHA state that these numbers only serve as a guideline and the “goal is zero detectable Legionella in a water source”.

i ASHRAE Guideline 12 -2000
ii  U.S.Department of Labor OSHA Technical Manual Section III, Appendix III: 7-3

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