Legionella is a type of bacteria commonly found in natural freshwater environments like lakes and streams. It can become a health concern when it grows to higher numbers in human-made water systems. Understanding how temperature influences its growth and survival is important for controlling its presence. This article explores the conditions that favor Legionella proliferation and the temperatures necessary to eliminate it.
Legionella’s Preferred Living Conditions
Legionella bacteria thrive and multiply rapidly within a specific warm water temperature range. This optimal growth range is typically between 20°C and 45°C (68°F and 113°F). Its most prolific growth occurs around 35°C to 37°C (95°F to 98.6°F).
Below 20°C (68°F), Legionella can survive but becomes dormant. However, if temperatures later rise into the favorable range, the bacteria can reactivate and begin to multiply. These conditions are frequently met in various man-made water systems, including hot water tanks, cooling towers, hot tubs, and plumbing systems with stagnant water.
The Lethal Temperatures for Legionella
To effectively control Legionella, understanding the temperatures that inhibit its growth or kill the bacteria is important. Temperatures above 50°C (122°F) begin to inhibit Legionella growth, and the bacteria will start to die off. The rate at which the bacteria are killed increases significantly with rising temperatures.
At 50°C (122°F), it can take between 80 to 124 minutes to kill 90% of Legionella bacteria. Raising the temperature to 55°C (131°F) can kill 90% of the bacteria in approximately 20 minutes, while 100% can be eliminated over five to six hours. At 60°C (140°F), 90% of Legionella can be killed in just two minutes, and at 70°C (158°F), the bacteria are destroyed almost instantly. Maintaining hot water storage tanks at or above 60°C (140°F) is a common strategy to prevent Legionella growth, though safety measures like thermostatic mixing valves at outlets are necessary to prevent scalding.
Practical Steps for Prevention
Controlling Legionella involves measures beyond understanding lethal temperatures. Maintaining appropriate water temperatures throughout a system is a primary step. Hot water should be stored at a minimum of 60°C (140°F) and circulated to ensure it reaches outlets at 50°C (122°F) or higher. Conversely, cold water systems should be kept below 20°C (68°F) to prevent bacterial growth.
Regularly flushing stagnant water from infrequently used fixtures, such as showerheads, faucets, and dead-end pipes, helps reduce conditions favorable for Legionella growth. Cleaning and disinfecting water system components, including showerheads, aerators, and hot tubs, contributes to prevention. For larger, more complex systems like cooling towers, routine maintenance and professional checks are important to minimize risk.
Understanding Legionnaires’ Disease
Legionnaires’ disease is a severe form of pneumonia caused by Legionella bacteria. This illness occurs when individuals inhale tiny water droplets, or aerosols, contaminated with the bacteria. These contaminated aerosols can originate from various sources, including showerheads, hot tubs, cooling towers, and decorative fountains.
Legionnaires’ disease is not contagious and cannot be spread directly from person to person. Symptoms typically appear 2 to 10 days after exposure and can include fever, cough, shortness of breath, muscle aches, and headaches. Seeking medical attention is important if exposure is suspected and these symptoms develop.