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what is legionnaires’ disease

Updated Oct 20, 20262 min readAnswer
On this pageShort answer How Legionnaires disease is treated Common questions Related questions Sources
Short answer

Legionnaires’ disease is a serious type of pneumonia caused by breathing in tiny water droplets that contain Legionella bacteria.

The bacteria grow in building water systems, so common sources include hot tubs, cooling towers, large or complex plumbing, decorative fountains, and humidifiers. Symptoms look like other pneumonias: cough, fever, chills, shortness of breath, muscle aches, and headache, sometimes with diarrhea, nausea, or confusion. They usually begin 2 to 14 days after exposure, so it helps to tell your clinician about recent travel, hotel stays, hot tub use, or hospital care. A urine test or a sputum culture confirms it, and antibiotics work best when started early. A milder form of the same infection, called Pontiac fever, causes fever and aches without pneumonia and clears on its own.

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How Legionnaires disease is treated

1Act on breathing symptoms:Fever with cough or shortness of breath needs a same-day clinician visit, and severe breathing trouble, chest pain, or confusion needs emergency care.
2Share your exposures:Mention any travel, hotel or cruise stay, hot tub use, or recent hospital stay in the past two weeks, since that changes which tests get ordered.
3Ask about the right test:A urine antigen test plus a sputum culture is the standard way to confirm Legionella, and a chest X-ray shows whether you have pneumonia.
4Finish the antibiotics:Take the full course even after you feel better, and tell your clinician if fever or breathlessness is not improving after a few days.
5Maintain home water systems:Keep hot water hot, flush taps and showerheads that have not been used for a week or more, and follow the disinfectant and cleaning instructions for any hot tub.
6Know your higher-risk groups:People over 50, current or former smokers, and those with chronic lung disease or weakened immunity should seek care early rather than waiting it out.

Common questions

what is legionnaires’ disease

Legionnaires’ disease is a lung infection caused by Legionella bacteria, which grow in building water systems such as hot tubs, cooling towers, large plumbing systems, decorative fountains, and humidifiers. You get it by breathing in contaminated water mist or droplets, not from other people. Symptoms usually start 2 to 14 days after exposure and include cough, fever, shortness of breath, muscle aches, and headache. It is treated with antibiotics, and many people need hospital care. Risk is higher if you are 50 or older, smoke or used to smoke, or have chronic lung disease or a weakened immune system. Call a clinician promptly if you have pneumonia symptoms.

About this page. Written and maintained by the Pymander Health team. Last updated September 6, 2026.

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