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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. Typical symptoms include fever, fatigue, cough, and shortness of breath (Murdoch et. al, 2018). On physical examination, the patient may have rales or other signs of consolidation. Findings on imaging are varied and nonspecific; however, the most common findings are patchy unilobar 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.

According to Murdoch and colleagues (2018), 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

Testing

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 

Diagnosis

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

Treatment

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.

References

Centers for Disease Control (CDC) (2018). Legionella (Legionnaires' Disease and Pontiac Fever-For Clinicians. Retrieved from https://www.cdc.gov/legionella/clinicians.html

Murdoch, D., Chambers, S. T., & Priest, P. (2020). Clinical manifestations and diagnosis of Legionella infection. UpToDate. Retrieved July 8, 2020, from https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-legionella-infection?search=legionella&source=search_result&selectedTitle=2~103&usage_type=default&display_rank=2

Murdoch, D., Chambers, S. T., & Priest, P. (2020). Treatment and prevention of Legionella infection. UpToDate. Retrieved July 8, 2020, from https://www.uptodate.com/contents/treatment-and-prevention-of-legionella-infection?search=legionella&source=search_result&selectedTitle=1~103&usage_type=default&display_rank=1