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vital signs - 9 in 10 CDC investigations show almost all outbreaks were caused by problems preventable with more effective wagter management.

Legionellosis outbreaks occur when two or more people are exposed to Legionella and get sick in the same place at about the same time. People can get legionellosis when they breathe in a mist (small droplets of water in the air) that is contaminated with Legionella.

Outbreaks are commonly associated with buildings or structures that have complex water systems, like hotels and resorts, long-term care facilities, hospitals, and cruise ships. The most likely sources of infection include water used for showering, hot tubs, decorative fountains and cooling towers (parts of centralized air-conditioning systems for large buildings).

Legionellosis outbreaks can be difficult to identify, especially if people travel to a common location, are exposed to Legionella, and then return home before becoming sick. State and local health departments take the lead in investigating outbreaks and implementing control measures to remove Legionella from the water identified as the source of infection. CDC is only involved in legionellosis outbreak investigations when additional assistance is requested. State and local health departments are the best source of information for a specific outbreak.

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