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Health Care Provider Information

Legionella-Legionnaires’ Disease and Pontiac Fever

Legionella-Legionnaire's Disease & Pontiac Fever

Clinical Features

Pneumonia caused by Legionella is clinically and radiologically similar to pneumonia caused by other pathogens. Symptoms of Legionnaires' disease develop 2-10 days after exposure to the bacteria occurs. Multiple sources denote that fever, fatigue, cough, and shortness of breath are the most predominant symptoms of disease. On physical examination, rales may be notable when assessing the lung sounds and other signs of consolidation may be present. Findings on imaging are varied and nonspecific; however, the most common findings are patchy infiltrates. Patients may also have low sodium levels, increased LFTs & CRP, as well as poor response to beta-lactam monotherapy. Extrapulmonary disease may occur and includes cellulitis, skin abscesses, septic arthritis, myocarditis, or endocarditis.

Pontiac fever is typically self-limiting and pneumonia does not develop. Symptoms include fever, chills, myalgia, malaise, headache, fatigue, nausea and/or vomiting.


Risk Factors

Risk factors identified by the CDC for legionella infection includes:

  • Age >50 Years
  • Current or Past Smoker
  • Chronic Lung Disease
  • Immunosuppression
  • Cancer
  • Chronic Disease
  • Recent Travel or Hospitalization
  • Exposure to Hot Tub


The CDC notes the following indications for further testing for Legionnaires' disease:

  • Failure of antibiotic therapy for community-acquired pneumonia
  • Severe pneumonia requiring ICU admission
  • Immunocompromised patients with pneumonia
  • Travel history within the last 10 days of symptom onset
  • During disease outbreak
  • Healthcare-associated pneumonia
    • onset of pneumonia is >48 hours after admission
    • other patients within the same facility have had a diagnosis of Legionnaires' disease within the past 12 months
    • positive environmental tests for Legionella within the last 2 months
    • current changes in water quality within the facility 


According to the CDC, best practice is to obtain both sputum culture and a urinary antigen test concurrently.

Gold Standard Testing: 

  • Culture of lower respiratory secretions on selective media
    • Sputum
    • Bronchoalveolar lavage
  • Urinary antigen test
  • Serological tests are not recommended in most cases


Check for updates on the IDSA-ATS practice guidelines for treatment of  CAP and HAP. Macrolides and respiratory fluoroquinolones are currently the preferred choice of treatment. Pontiac fever does not require antibiotic treatment.

Precautions, Identification, & Prevention

Precautions: No isolation or contact precautions are necessary

Identification: A single case of Legionella infection warrants suspicion of an outbreak. Investigation is typically conducted by hospital epidemiologists or local public health departments. 

Prevention: Testing and water disinfection are routine practices in water distribution systems in the United States.


Centers for Disease Control (CDC) (2018). Legionella (Legionnaires' Disease and Pontiac Fever-For Clinicians. Retrieved from

Murdoch, D., Chambers, S. T., & Priest, P. (2020). Clinical manifestations and diagnosis of Legionella infection. UpToDate. Retrieved July 8, 2020, from

Murdoch, D., Chambers, S. T., & Priest, P. (2020). Treatment and prevention of Legionella infection. UpToDate. Retrieved July 8, 2020, from