Legionellosis is a group of diseases that includes legionnaires’ disease. The potentially fatal infection has symptoms similar to flu and pneumonia. Legionella pneumophila, the bacteria responsible for legionnaires’ disease, exist naturally in external watercourses, and can easily transfer to water used in buildings through air-conditioning and recirculated hot and cold water systems. In certain conditions, bacteria can multiply to critical levels in stored water.

Legionnaires’ disease is caused when water droplets containing the bacteria are inhaled. This topic describes how to manage the risk from legionella bacteria in such systems.

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