Cooling Towers and Legionnaires’ Disease
What is a cooling tower? A cooling tower is a component of large scale cooling operation (e.g. central cooling plant). A cooling tower uses recirculated water to remove heat from a building or group of buildings. Water is recirculated because it is unnecessary, extremely wasteful and prohibited by law to use once-through water for this type of application. However, this recirculated water provides an environment in which bacteria that cause Legionellosis thrive. For this reason, a multi-faceted system of registration, maintenance, monitoring and inspection has been implemented to control biological contaminants and prevent cooling towers from being a source of exposure to pathogenic bacteria.
What is Legionellosis? Legionellosis is a respiratory disease caused by Legionella bacteria. Sometimes the bacteria cause a serious, sometimes fatal type of pneumonia called Legionnaires' disease. The same bacteria can also cause a less serious infection (but without pneumonia) called Pontiac fever that has symptoms similar to a mild case of the flu. With proper diagnosis and early treatment, people with Legionnaires' disease often survive.
Most people exposed to the Legionella bacteria do not develop illness. Those at higher risk of developing Legionnaires' disease are people with impaired lung function (e.g. smokers, persons with COPD, asthma); weakened immune systems due to underlying illness, organ transplant, immunosuppressive medications; and the elderly. Persons who are already hospitalized are at greater risk; this increased risk has been long recognized by NYS DOH, which has issued guidelines for control of Legionellosis from environmental sources .
How are cooling towers maintained and regulated in New York? An outbreak of Legionnaires’ disease in a localized area of the south Bronx in August 2015 was traced back to building cooling towers in the area. By September 2015, NYC and NYS established a regulatory framework that built upon existing best practices for cooling tower operation to minimize/prevent future outbreaks.
Cooling towers are carefully maintained both to ensure proper functioning of the equipment and prevention of biological growth (including Legionella). The various maintenance/monitoring tasks are performed by in-house staff wherever possible and outside contractors wherever required/mandated by regulations.
Biocides are continually added to cooling tower water and monitored for effectiveness. Cooling towers are inspected visually each week. Cooling tower water is sampled and analyzed at least quarterly specifically for the presence of Legionella; a positive test triggers remediation measures (disinfection, cleaning and re-testing) whether or not the contamination has resulted in an outbreak. Engineers perform less specific tests (that detect bacterial presence without identifying the species) several times each week. Annual certification is performed by an outside contractor. Documentation of maintenance and monitoring are submitted to NYC DOHMH. Cooling towers are inspected annually by NYC DOHMH personnel.
Useful links
- The 2015 New York City Legionnaires' Disease Outbreak: A Case Study on a History-Making Outbreak
- NYC Health: Health Topics: Legionnaires’ Disease
- NYS Department of Health: Legionnaires' Disease and Legionella
- Centers for Disease Control and Prevention (CDC): Legionella (Legionnaires' disease and Pontiac Fever)
- OSHA Legionnaires' disease eTool
