Where are legionella bacteria that cause Legionnaires' disease most likely to be found?

Legionella bacteria thrive in warm, stagnant water environments, which is why they are often associated with infrequently used plumbing fixtures. An infrequently used shower hose outlet is particularly conducive to the growth of these bacteria because water that remains stagnant allows the bacteria to proliferate. When someone eventually uses the shower, the aerosolized droplets can be inhaled, potentially leading to Legionnaires' disease.

In contrast, frequently used taps generally have fresh water flowing through them, making it less likely for conditions conducive to Legionella growth to develop. A regularly cleaned swimming pool typically employs chlorine and filtration systems that help eliminate bacteria, including Legionella. Lastly, a hot water heater set to high temperatures (above 60°C or 140°F) provides an environment that can kill Legionella, as the bacteria do not thrive in high-temperature water. Thus, the likelihood of finding Legionella is significantly higher in infrequently used outlets, where stagnant water provides an ideal breeding ground for the bacteria.