Legionella bacteria can be found in a variety of naturally occurring sources (i.e., soils, ponds and
streams) in addition to man made sources such as cooling towers, potable water systems and
heating, ventilation and air-conditioning (HVAC) systems. Legionella bacteria are present in
public and well water supplies at extremely low concentrations. Legionella bacteria grow well in
cooling towers and other indoor water systems primarily because of warm water and available
nutrients. This warm water can promote the growth of algae, microbiological “slime” and
amoebae if not properly treated, which enhance the potential for Legionella bacteria
amplification.
Following the 1976 American Legion Convention at the Bellevue Stratford Hotel in
Philadelphia, 34 attendees died and 221 people became ill from pneumonia caused by the
bacterium Legionella pneumophila. This disease, now commonly known as Legionnaires’
Disease, is a respiratory infection that strikes susceptible individuals exposed to virulent Legionella bacteria. Infection results from inhaling airborne water droplets or mist containing
viable, disease causing Legionella bacteria, which are small enough to pass deep into the lungs
and be deposited in the alveoli, the small pockets in the lungs. The dose of Legionella pneumophila and other Legionella bacteria required to infect humans is not definitively known.
Legionnaires’ Disease can have an incubation period of two to ten days. Although healthy
individuals may develop Legionnaires’ Disease, people thought to be at increased risk of
infection include smokers, patients with cancer, chronic respiratory diseases, kidney disease, and
any immuno-suppressed condition.
The purpose of a Legionella Control Program is to minimize the presence of Legionella bacteria
and other environmentally associated bacteria in building waterside systems and consequently
reduce the potential for illnesses associated with these organisms. The mechanisms to achieve
the above are to limit the ecological conditions (temperature range and nutrients) and physical
plant (design) operations and maintenance issues that allow the Legionella bacteria to grow and
amplify. However, please note that the complete elimination of Legionella bacteria in building
water systems may not be possible. As such, instituting preventive maintenance procedures are a
critical aspect of Legionella bacteria control. A well designed control program includes the
following information:
- Source Identification - Review design, operations and maintenance of waterside systems
i.e.; hot water tanks, cooling towers, HVAC systems, humidifiers, piping networks,
process water and distribution systems for source identification and to perform a risk
assessment to determine the likelihood of the system(s) harboring Legionella bacteria and
the potential for exposure to aerosolized water droplets or mists.
- Preventive Maintenance – Develop site specific guidelines for preventative
maintenance procedures for each of the waterside systems for cleaning and maintenance
of environmental conditions such as temperature ranges and water treatments to reduce
the potential for the amplification of Legionella bacteria.
- Sampling and Analytical Procedures, and Data Interpretation - Determine the best
practices for water sampling locations, frequency of sampling and data interpretation in
relation to preventative maintenance procedures and risk assessment.
- Decontamination Guidelines – Develop site specific guidelines for decontamination of
each waterside system including mechanical cleaning, chemical treatment options and
heat pasteurization techniques.
- Emergency Response Procedures – Identify the appropriate team members from within
the facility and outside resources including: facilities/physical plant personnel, safety,
medical component, experienced industrial hygiene consultant, environmental laboratory,
chemical treatment vendor, and field sample collection to completely respond to high
concentrations of Legionella bacteria in samples or an Legionnaire’s disease outbreak.
For additional information or to request a proposal, please contact Harry M. Neill, CIH, Vice
President at 888.873.9983 ext 15, www.1ssh.com, or at hneill@1ssh.com.