what is legionnaires’ disease
Last updated September 6, 2026.
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.
What to do
- Act 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.
- Share 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.
- Ask 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.
- Finish 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.
- Maintain 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.
- Know 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.
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