What are the symptoms of Legionnaires' disease?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Legionnaires' disease is a serious form of pneumonia caused by Legionella bacteria. Common symptoms include high fever, chills, a dry or productive cough, shortness of breath, muscle aches, headaches, and in some cases, confusion, nausea, or diarrhea. Symptoms typically appear 2–10 days after exposure and can escalate quickly, making early recognition critical.

Because these symptoms closely mirror the flu, COVID-19, and other respiratory illnesses, self-diagnosis can be difficult—and delaying care can be dangerous. If you're experiencing any combination of these symptoms, take a free, instant, online symptom check to better understand what may be causing them and get clear guidance on your next steps.

Reviewed for medical accuracy: 07/20/2026

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Explanation

Legionnaires' disease is a type of pneumonia caused by Legionella bacteria. People with this illness often start with symptoms like fever, chills, and a cough. These symptoms can be similar to the flu. As the disease progresses, it can cause muscle aches, headaches, and sometimes confusion or changes in mental state.

Common Symptoms:

Fever and Chills: These are often the first signs and can be quite severe.
Cough: This may be dry or produce mucus.
Muscle Aches: General body pains are common.
Headache: This can accompany other symptoms.
Confusion: Some people may experience changes in their mental state.

These symptoms can vary in severity, and not everyone will have all of them. If you're experiencing any combination of these symptoms and want to better understand what might be causing them, try our free AI symptom checker to help guide your next steps before seeing a healthcare provider for proper diagnosis and treatment.

(References)

Pancer K. (2010). [Legionnaires' disease--risk factors and symptoms]. Przeglad epidemiologiczny, 20731241.
Tsai TF, Finn DR, Plikaytis BD, McCauley W, Martin SM, & Fraser DW. (1979). Legionnaires' disease: clinical features of the epidemic in .... Annals of internal medicine, 434627.
Kirby BD, Snyder KM, Meyer RD, & Finegold SM. (1978). Legionnaires' disease: clinical features of 24 cases. Annals of internal medicine, 686539.

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