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Written by Robert E. Sheriff, MS, CIH, CSP, President
August 11, 2015, Updated June 2019
The Spread of Legionella Bacteria Through Cooling Towers
The much-publicized outbreak of Legionnaires’ Disease in New York City from cooling towers is not the only way Legionella Bacteria can grow and infect humans. Yes, cooling towers are a very likely place where Legionella pneumophila can propagate and infect humans. First, they are in an ideal environment for the Legionella bacteria to grow. This bacteria likes warm water (between 90 and 115°F) (not hot! not cold). A cooling tower lowers the temperature of hot water, but it’s still very warm. A cooling tower takes very warm or hot water and cools it down but usually only from very warm/hot to a lower temperature but not cold. The end result is warm water with dirt or debris creating an ideal “culture plate” for Legionella pneumophila. Cooling towers spray hot water into the air, so a mist is formed. If this water is contaminated with Legionella bacteria, the mist can spread over a wide area and can be inhaled by passers-by, residents, shoppers, etc.
Who Is At Risk?
Most healthy individuals will not be seriously affected by the Legionella bacteria: flu-like symptoms—low to moderate fever, aches, stuffiness, general malaise are possible. Most people will recover in a few days. However, the very young, the very old, or those already weakened due to illness or injury, are at great risk of serious illness or even death. Treatment is generally with antibiotics since it is bacteria.
It is understood that in the Bronx, NY outbreak the New York City Health Department is arranging for free water tests and will require treatment of cooling towers.
It is important to note that cooling towers are not the only environment where Legionella can survive, multiply and infect humans.
Other Sources Where Legionnaires Disease Can Spread
Hot water heaters are another likely source, especially where the hot water system is kept in the “warm” range (100-120°F) so as not to scald children, the elderly, or the sick. Examples are daycare facilities, hospitals, and senior citizen housing. Bacteria can propagate at the bottom of a water heater where calcium build-up can further reduce water temperature and retain debris for the bacteria to consume. The same can be true of shower heads and lesser used sinks or tubs AND ESPECIALLY HOT TUBS! Humidifiers are also a source of bacterial growth if not kept clean.
The most common infections where someone becomes seriously ill is in senior citizens housing or healthcare facilities.
Once Legionella pnuemophila is found, it is very difficult to eliminate. A single slugging with chlorine or other disinfectant is generally not successful or is only a temporary fix. Often complete replacement of the hot water heater, replacing fixtures and vigorous treatment with disinfectants is the only permanent fix.
Locating The Source
Another problem is just finding the sources. There are often many places in a water system where the water temperature is in a range where incubation can take place, making it very difficult to locate the true source of the problem.
Sampling, Testing, and Prevention
Prevention and regular sampling/testing are the best solutions. Keeping hot water systems, hot tubs, humidifiers clean and free of calcium build-up, maintaining hot water temperature at 120°F or greater (beware over about 130°F can scald the skin), testing of hot water systems and cooling towers—annually or at least every few years—and reacting rapidly to a positive test of a person for Legionnaires’ Disease is essential.
We have staff personnel with experience in testing water systems and dealing with known Legionella bacteria sites.
For more information, refer to the other articles on Legionnaires’ Disease on our website at https://www.atlenv.com/ or contact us at 800-344-4414. You may also fill out our online contact form to get in touch.
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