Water Treatment

Legionella: Mitigating the Risk

May 3rd, 2019

    Legionella bacteria has made the news quite often in recent years due to outbreaks all over the world. These outbreaks have spanned the globe from Surrey, BC, to Disneyland and Brescia, Italy. Exposure to Legionella bacteria is what leads to Legionnaires’ Disease (also Legionellosis), which can sometimes be fatal. A September 2018 Legionnaires’ outbreak in Italy resulted in the hospitalization of 405 people and 2 confirmed deaths. The cause was investigated and linked back to cooling towers that spread the Legionella bacteria through the aerosolization of cooling water.  British Columbia has recorded several Legionella cases over the years. The most recent outbreak occurred in late 2018 and resulted in 7 confirmed illnesses.


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Water treatment and microbial testing of cooling towers and condensers is critical to keep Legionella bacteria from multiplying.

     The Center for Disease Control (CDC) stated that “9 in 10 investigations show almost all outbreaks were caused by problems preventable with more effective water management.” Regular testing and water maintenance are of high importance because of how Legionella spreads to cause illness. Cooling towers use water as the heat transfer medium to provide comfort or process cooling.  System water is cooled through evaporation within the tower, creating a warm, stagnate environment which is ideal for bacteria growth.  If legionella is present and allowed to grow through improper water management, the aerosolized mist created by the cooling process will spread the bacteria to the surrounding area and into buildings via air intake systems. Inhalation of the aerosolized legionella bacteria can lead to a severe form of pneumonia (Legionnaires’ disease), which can result in hospitalization or even death for immunocompromised individuals.    


People who are more susceptible to Legionnaires’ are smokers, those affected by chronic lung issues, and people of advanced age, according to CDC.

      How can we minimize the risk of spreading Legionella from the cooling tower? The first step is to test the cooling tower water on a regular basis. Public Works and Government Services Canada recommends, “Weekly dipslide tests to determine the total bacteria count (TBC) at each water sampling location. While the system is in normal operation, perform monthly Legionella bacteria culture tests to identify total Legionella pneumophila including all serogroups (LPTOT) bacteria levels.” The second step is to determine a water management and sanitization program to minimize bacterial growth in the cooling tower. This can include a clean out and disinfection of a system upon initial start-up and after shut-down (twice yearly) along with a comprehensive ongoing water treatment program for corrosion and bacteria control.

     CDC states that “There is no known safe level of Legionella in building water systems. The intent of a water management program should be to manage building water systems to reduce the hazardous conditions that allow the Legionella to grow and spread to susceptible people.” To contain and prevent further spread of the respiratory disease-causing bacterium, Legionella, owner/operators can work with local water treatment specialists like PACE Chemicals to determine the best management plan for their cooling towers.


CDC: https://www.cdc.gov/legionella/outbreaks.html


PWGSC: https://www.tpsgc-pwgsc.gc.ca/biens-property/legionalla/chapitre-chapter-3-eng.html#c35

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