A plain-English look at Legionnaires' disease symptoms, how soon they show up after exposure, and when it's time to see a doctor.
Legionnaires' disease symptoms often start out looking like a bad flu or a chest cold, which is part of what makes this illness easy to miss at first. According to the CDC, Legionnaires' disease is a serious form of pneumonia caused by Legionella bacteria, and it's caught by breathing in contaminated water droplets, not by drinking water or from person-to-person contact. Below is a plain-English rundown of what to watch for, how symptoms usually progress, and when it's time to get checked out.
What are the symptoms of Legionnaires' disease?
The most common symptoms of Legionnaires' disease, according to the CDC, include:
- Cough
- Fever, sometimes high
- Chills
- Shortness of breath
- Muscle aches
- Headache
Some people also develop diarrhea, nausea, loss of appetite, or confusion. Because Legionnaires' disease is a lung infection, chest X-rays typically show pneumonia, and the illness can range from mild to severe. Left untreated, it can lead to respiratory failure and can be fatal.
How long after exposure do symptoms appear?
Symptoms of Legionnaires' disease usually appear 2 to 14 days after exposure, according to the CDC. That's the incubation period between breathing in contaminated water droplets and the first signs of illness. This gap is one reason outbreak investigators like NYC Health ask people where they spent time, and for how long, in the two weeks before they got sick — it helps map possible exposure windows, though it doesn't by itself identify where any one person was exposed.
Early symptoms vs. severe symptoms
Legionnaires' disease often starts quietly. Early symptoms can look a lot like the flu: mild fever, headache, muscle aches, and general fatigue. Over the next day or two, symptoms typically become more severe:
- A high fever, sometimes 104°F or higher
- A worsening cough, which may bring up mucus or blood
- Increasing shortness of breath
- Chest pain, especially when breathing deeply or coughing
- Confusion or other changes in mental state, in some cases
Because the early symptoms overlap with common respiratory illnesses, people sometimes wait to seek care, which can allow the infection to progress. Getting evaluated promptly matters. This page offers general information, not medical or legal advice — talk to a doctor about your symptoms, and if you're considering next steps after a diagnosis, talk to an attorney about your specific situation.
When should you see a doctor or go to the ER?
See a doctor promptly if you develop fever, cough, and shortness of breath, especially if in the two weeks before symptoms started you spent time near a cooling tower, hot tub, decorative fountain, or in a building with complex plumbing or hot-water systems — including anywhere in the Carnegie Hill and Yorkville area of Manhattan during the 2026 Upper East Side Legionnaires' outbreak. Tell your doctor about any recent travel, hotel stays, or hospital visits, since these are common ways people are exposed.
Go to the emergency room, or call 911, for:
- Severe or worsening shortness of breath
- Chest pain
- Confusion or disorientation
- A high fever that doesn't respond to medication
- Bluish lips or face
Who is at higher risk?
Anyone can get Legionnaires' disease, but according to the CDC, some people face a higher risk of severe illness, including people who:
- Are age 50 or older
- Currently smoke or used to smoke
- Have chronic lung disease
- Have a weakened immune system, including from certain medications or medical conditions
People in these groups who develop pneumonia-like symptoms after a possible exposure should seek medical care promptly.
How is Legionnaires' disease diagnosed?
Doctors typically diagnose Legionnaires' disease by pairing a urinary antigen test with a lower-respiratory culture or molecular (PCR) test, which is the approach the CDC recommends. Treatment with antibiotics generally shouldn't wait for test results if a doctor suspects Legionnaires' disease. For a closer look at how testing works and what each test does and doesn't tell you, see our guide to Legionnaires' disease testing and diagnosis.
For general background on the illness itself, including how it spreads and how outbreaks are investigated, see our Legionnaires' disease guide.
If you or a family member has been diagnosed with Legionnaires' disease, Traction Law Group offers a free, confidential case review, and you pay nothing unless we recover money for you. Contact us to talk through your situation.
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Frequently Asked Questions
Symptoms usually appear 2 to 14 days after exposure to contaminated water droplets, according to the CDC. This is called the incubation period.
Early signs often resemble the flu: fever, headache, muscle aches, and fatigue, followed within a day or two by a worsening cough and shortness of breath.
Recovery time varies. Mild cases treated early with antibiotics may improve within a couple of weeks, while severe cases requiring hospitalization can take longer, and some people face lasting complications.
No. According to the CDC, Legionnaires' disease is not normally spread from person to person. People get it by breathing in contaminated water droplets, not from being near someone who is sick.
Yes. A milder illness caused by the same bacteria is called Pontiac fever. It causes flu-like symptoms without pneumonia and typically resolves on its own without antibiotics, unlike Legionnaires' disease.
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