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(Legionnaires' Disease and Pontiac Fever)

Home > Top 10 things every clinician needs to know about Legionellosis

Top 10 Things Every Clinician Needs to Know About Legionellosis

 

1.

What does the diagnosis of Legionellosis include?

  Two clinical syndromes: Legionnaires' disease and Pontiac fever.
 
  Legionnaires' disease Pontiac fever
Clinical features Pneumonia: cough, fever, chest pain Flu-like illness (fever, chills, malaise) without pneumonia
Radiographic pneumonia Yes No
Incubation period 2-14 days after exposure 24-48 hours after exposure
Etiologic agent Legionella species Legionella species
Attack rate* < 5% > 90%
Isolation of organism Possible Virtually never
Outcome

Hospitalization common

Case-fatality rate: 5-40%**

Hospitalization uncommon

Case-fatality rate: 0%

* Percent of persons who, when exposed to the source of an outbreak, become ill.

** Percent of persons who die from Legionnaires' disease or Pontiac fever.

   

2.

Who should be tested for Legionnaires' disease?

  View IDSA guidelines (exit site)
 
  • Hospitalized patients with enigmatic pneumonia
  • Patients with enigmatic pneumonia sufficiently severe to require care in the ICU
  • Compromised host with pneumonia
  • Patients with pneumonia in the setting of a legionellosis outbreak
  • Patients who fail to respond to treatment to a ß-lactam or cephalosporin
  • Patients with a travel history [Patients that have traveled away from their home within two weeks before the onset of illness.]
  • Patients suspected of nosocomial pneumonia with unknown etiology

3.

How do I test for Legionnaires' disease?

  • Urinary antigen assay AND culture of respiratory secretions on selective media are the preferred diagnostic tests for Legionnaires' disease
  • Sensitivity and specificity of diagnostic tests
   
Test
Sensitivity (%)
Specificity (%)
Culture
80
100
Urine antigen
70
100
Paired serology*
70-80
>90
Direct fluorescent antibody stain
25-75%
95
* Note: A single antibody titer of any level is not diagnostic of legionellosis.

 

4.

Why is it important to obtain a respiratory specimen for culture of possible Legionella infection?

 

Isolation of Legionella from respiratory secretions, lung tissue, pleural fluid, or a normally sterile site is still an important method for diagnosis, despite the convenience and specificity of urinary antigen testing. Investigations of outbreaks of Legionnaires' disease rely on both clinical and environmental isolates. Clinical and environmental isolates can be compared using monoclonal antibody and molecular techniques. Because Legionella are commonly found in the environment, clinical isolates are necessary to interpret the findings of an environmental investigation.

5.

What is the preferred treatment for Legionnaires' disease?

 
  • If your patient has Legionnaires' disease, please see the most recent guidelines (exit site) from IDSA for community-acquired pneumonia.
  • For patients with Pontiac fever: it is a self-limited illness that does not benefit from antibiotic treatment. Complete recovery usually occurs within 1 week.

6.

Why do I need to ask patients about travel in the 14 days before onset of disease?

  Although outbreaks of travel-associated legionellosis are infrequently identified, more than 20% of all cases are thought to be associated with recent travel. Outbreaks of Legionnaires' disease among travelers are difficult to detect because of the low attack rate, long incubation period, and the dispersal of persons from the source of the outbreak. Timely reporting of travel-associated cases could allow early identification and control of known sources of infection.
 

7.

How common is Legionnaires' disease?

  Each year an estimated 8,000-18,000 hospitalized cases occur in the U.S. However, accurate data reflecting the true incidence of disease are not available because of underutilization of diagnostic testing and under-reporting. It is a common cause of severe pneumonia requiring hospitalization. The majority of reported cases are sporadic. Travel-associated outbreaks, outbreaks in community settings, and nosocomial and occupational outbreaks are common.
 

8.

Where do Legionella come from?

 

Legionella can be found in natural, freshwater environments, but they are present in insufficient numbers to cause disease. Potable (drinking) water systems, whirlpool spas, and cooling towers provide the 3 conditions needed for Legionella transmission-heat, stasis, and aerosolization; therefore, these are common sources of outbreaks.

9.

What are epidemiologic risk factors for legionellosis?

 
  • Recent travel with an overnight stay outside of the home
  • Exposure to whirlpool spas
  • Recent repairs or maintenance work on domestic plumbing
  • Renal or hepatic failure
  • Diabetes
  • Systemic malignancy
  • Smoking
  • Immune system disorders

10.

How should you report Legionellosis?

 

Legionellosis is a nationally notifiable disease.

Report cases of Legionellosis to your local or state health department.

  1. Find your state health department .
  2. Download case report form as a PDFAdobe Acrobat (PDF 21KB)

Call, fax, or mail this information to your local or state health department within 7 days of diagnosis. Prompt reporting could allow early identification and control of known sources of infection.

 

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Page Last Modified: April 22, 2008
Content Source: National Center for Immunization and Respiratory Diseases

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