Diagnosis, Treatment, and Complications

Legionellosis can present as two types of illness: Legionnaires’ disease and Pontiac fever. The two illnesses can be diagnosed with similar tests, but are treated differently.

Legionnaires’ Disease


People with Legionnaires’ disease have pneumonia (lung infection), which can be confirmed by chest x-ray. Clinicians typically use two preferred types of tests to see if a patient’s pneumonia is caused by Legionella:

Elderly woman sick in bed
  • Urine test
  • Laboratory test that involves taking a sample of sputum (phlegm) or washing from the lung

Treatment and Complications

Legionnaires’ disease requires treatment with antibiotics (medicines that kill bacteria in the body), and most cases of this illness can be treated successfully. Healthy people usually get better after being sick with Legionnaires’ disease, but they often need care in the hospital.

Possible complications of Legionnaires’ disease include

  • Lung failure
  • Death

About 1 out of every 10 people who gets sick with Legionnaires’ disease will die due to complications from their illness.1  For those who get Legionnaires’ disease during a stay in a healthcare facility, about 1 out of every 4 will die.2

Pontiac Fever


Clinicians can use a urine or blood test to see if someone has Pontiac fever. However, a negative test doesn’t rule out that someone may have it (this is called a false negative). Clinicians most often diagnose Pontiac fever when there are other known laboratory-confirmed legionellosis cases (either Legionnaires’ disease or Pontiac fever) who may have been exposed to Legionella at the same time or place.

Treatment and Complications

Pontiac fever goes away without specific treatment.



  1. Dooling KL, Toews KA, Hicks LA, et al. Active Bacterial Core surveillance for legionellosis—United States, 2011–2013. MMWR Morb Mortal Wkly Rep. 2015;64(42):1190–3.
  2. Soda E, Barskey A, Shah P, et al. Vital Signs: Health care-associated Legionnaires’ disease surveillance data from 20 states and a large metropolitan area — United States, 2015. MMWR Morb Mortal Wkly Rep. 2017; 66(22);584–9.

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