Clinical Guidance for Legionella Infections

Key points

  • Legionnaires' disease cannot be clinically or radiographically distinguished from pneumonia due to other pathogens.
  • Appropriate testing must be performed to make the correct diagnosis and inform treatment decisions.
  • The first-line treatment for healthcare-associated or community-acquired pneumonia doesn't always include Legionella-directed antibiotics.
Legionnaires' disease cannot be clinically or radiographically distinguished from pneumonia due to other pathogens.

Indications for Legionnaires' disease testing

For patients with pneumonia, the following indications warrant testing for Legionnaires' disease:

  • Outpatient antibiotic failure for community-acquired pneumonia
  • Severe pneumonia, in particular illness requiring intensive care
  • Presence of an immunocompromising condition
  • Overnight travel away from the home during incubation period
  • Risk factors and hospitalization with healthcare-associated pneumonia
  • Overnight stay in a healthcare facility during incubation period
  • Epidemiologic link to a setting with known Legionella concerns

Settings with concerns include those where Legionella has been identified or association with at least one laboratory-confirmed Legionnaires' disease case.

Defining the incubation period‎

For surveillance purposes, public health officials collect exposure histories for the 14 days before date of symptom onset.

Testing for healthcare-associated Legionnaires' disease is especially important if any of the following are identified in a healthcare facility:

  • Healthcare-associated Legionnaires' disease diagnosis in the last year
  • Positive environmental tests for Legionella
  • Recent changes in water quality that may lead to Legionella growth

Importance of asking about healthcare and travel exposures

The majority of recognized Legionnaires' disease outbreaks are associated with:

  • Healthcare settings: Hospitals, long-term care facilities1
  • Travel: Hotels, resorts, cruise ships1

Healthcare-associated cases: Timely reporting ensures steps can be taken to protect these highly susceptible populations.

Travel-associated cases: Approximately 10–15% of all reported cases of Legionnaires' disease occur in people who have traveled during their exposure period. Outbreaks among travelers can be difficult to detect because of

  • The low attack rate
  • The time interval between exposure and symptom onset
  • Dispersal of people from the source of the outbreak
  • Underdiagnosis of cases

Therefore, collecting and reporting information about overnight travel is important.

Keep Reading: Report Cases


The preferred diagnostic tests for Legionnaires' disease are both of the following paired together:

  • Culture of lower respiratory secretions
  • Legionella urinary antigen test

Lower respiratory secretions include sputum and bronchoalveolar lavage.

Specimen collection

Best practice is to obtain both sputum for culture and urine for the urinary antigen test concurrently. Sputum should ideally be obtained prior to antibiotic administration, but antibiotic treatment shouldn't be delayed to facilitate this process.

Keep Reading: Laboratory Testing

Treatment options

Legionnaires' disease

See treatment guidance for

First line treatment doesn't always include Legionella-directed antibiotics (e.g., macrolides and respiratory fluoroquinolones). Obtaining diagnostic testing before antibiotic administration is preferred; however, antibiotic treatment shouldn't be delayed to facilitate this process.

Pontiac fever

Antibiotic treatment shouldn't be prescribed for Pontiac fever. It's a self-limited illness that doesn't benefit from antibiotic treatment. Patients usually recover within 1 week.


Fact sheets