National case definition: Legionnaires' disease and Pontiac fever (Legionellosis)


Date of last revision/review: May 2008

National notification

Only confirmed cases of disease should be notified.

Type of surveillance

Routine case-by-case notification to the federal level.

Case classification

Confirmed case

  • Clinical illness (see Clinical evidence section) with laboratory confirmation of infection:
    • isolation of Legionella species or detection of the antigen from respiratory secretions, lung tissue, pleural fluid or other normally sterile fluids
  • or
    • a significant (e.g. fourfold or greater) rise in Legionella species IgG titre between acute and convalescent sera
  • or
    • IgG titre > 1:128 against Legionella species
  • or
    • demonstration of L. pneumophila antigen in urine (see Laboratory comments section)

Probable case

Clinical illness with demonstration of Legionella species DNA

Laboratory comments

Jurisdictions should use a validated antigen detection test, and test interpretation must be in accordance with the manufacturer's instructions. The urinary antigen test (UAT) is widely used in Canada and internationally. UAT targets Legionella pneumophila serogroup 1 but is not validated to target other serogroups or species in the genus.

Few laboratories use culture with biochemical confirmation in conjunction with antigen detection. A limited number of laboratories currently participate in College of American Pathologists (CAP) and Clinical Microbiology Proficiency Testing (CMPT) proficiency testing programs.

Clinical evidence

Legionellosis comprises two distinct illnesses: Legionnaires' disease, characterized by fever, myalgia, cough and pneumonia, and Pontiac fever, a milder illness without pneumonia.

ICD code(s)

ICD-10 code(s)

  • A48.1 Legionnaire's Disease
  • A48.2 Pontiac Fever

ICD-9/ICD-9CM code(s)

  • 482.8 Legionnaire's Disease

Type of international reporting

Under Article 6 of the International Health Regulations (IHR) (2005), each State Party shall notify the World Health Organization (WHO) by way of the IHR National Focal Point, and within 24 hours of assessment of public health information, of all events which may constitute a public health emergency of international concern within its territory in accordance with the decision instrument (Annex 2 of the IHR), as well as any health measure implemented in response to those events.


Probable case definitions are provided as guidelines to assist with case finding and public health management, and are not for national notification purposes.


World Health Organization. International Health Regulations (2005). 3rd ed. Geneva, 2016, from

Previous case definitions

Canadian Communicable Disease Surveillance System: disease-specific case definitions and surveillance methods. Can Dis Wkly Rep 1991;17(S3).

Case definitions for diseases under national surveillance. CCDR 2000;26(S3).

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