Legionnaires’ disease (legionellosis) is a form of pneumonia caused by Legionnaires’ disease bacteria (LDB), or legionella. Water is the major natural reservoir for legionellae, and dangerous levels of the bacteria typically appear in man-made aquatic environments. Contraction of the disease occurs when a person inhales aerosolized legionella or drinks legionella-contaminated water. If infection occurs, symptoms usually appear within 2 to 10 days. There is no evidence that Legionnaire’s spreads from person-to-person contact, so outbreaks are typically associated with water-supply contamination.
To reduce the risk of future Legionnaires’ Disease outbreaks, NYC legislators have proposed stringent new regulations for cooling tower inspections, as well as sanctions for failure to comply with new standards.
New York City’s recent Legionnaires’ disease outbreak, which caused 12 deaths and left over 100 people sick, has many facilities concerned with legionella prevention. The CDC estimates that 8,000-18,000 people are hospitalized annually due to legionellosis. Incidents of the disease increased threefold between 2000 and 2009. However, it is also estimated that 90% of cases go unreported.
Special water treatment and cleaning procedures can reduce LDB in water systems to safe levels.
Consider a Risk Assessment When …
- It has been more than 2 years since the last risk assessment.
- There have been changes to the water systems.
- The building use has changed.
- There is new information about risks or control measures.
Checks indicate that control measures are no longer effective.
At low levels of contamination, the chance of getting Legionnaires’ disease from a water source is very slight. The risk increases greatly when the organism is able to reproduce to high concentrations in man-made water systems. Legionella inhabits water, and complex water systems in large buildings provide ideal conditions for the growth of the organism. Water heaters, cooling towers, foundtains, misting devices, humidifiers and warm, stagnant water are prime examples.
Hot water heaters have been found to be almost twice as likely to be contaminated with legionella as cooling towers. At temperatures between 68°-122°F the organism can multiply. Temperatures of 90°-105°F are ideal for growth. Rust (iron), scale, and the presence of other microorganisms can also promote the growth of legionella bacteria.
1. A list of water services plant and outlets.
2. Inspection of plant to assess cleanliness, general condition, and compliance with standard operating procedures.
3. Production of water system schematics.
4. Samples for the presence of legionella bacteria from various locations within the down service water systems or from evaporative cooling systems.
5. Samples for microbial analysis from various locations within the down service water systems (taps, tanks, etc.) or from evaporative cooling systems.
6. Temperature measurements taken from various locations within the down service water systems (showers, water heaters, taps, tanks, etc.).
7. pH measurements taken from various locations within the down service water systems or from evaporative cooling systems.
8. Identification of sources of risk.
9. Review of previous test results for the evaporative cooling system and any other risk systems tested.
10. Numerical assessment of level of risk.
11. Review of the existing System of Legionella Control to assess compliance with best-practice guidance or regulations, where applicable.
12. Documentation of procedures and practices.
Controlling the conditions that lead to legionella occurrence is crucial. Regularly maintain and clean cooling towers and evaporative condensers to prevent growth of LDB. This should include twice-yearly cleaning and periodic use of a safe and effective biocide such as chlorine.
Maintain domestic water heaters at 60°C (140°F). The temperature of the water should be 50°C (122°F) or higher at the faucet.
Avoid conditions that allow water to stagnate. Large water-storage tanks exposed to sunlight can produce warm conditions favorable to high levels of LDB. Frequent flushing of unused water lines will help alleviate stagnation.