National case definition: Measles

Date of last revision: May 2025
Date of last review: May 2025

National notification

All confirmed cases of disease should be notified. Probable case reporting is requested upon provincial/territorial discretion.

Type of surveillance

Active, weekly case-by-case notification (including zero-notification) by provincial and territorial ministries of health to the Canadian Measles/Rubella Surveillance System (CMRSS).

Case classification

Laboratory- confirmed case

Laboratory confirmation of infection (in the absence of identification of measles vaccine strain based on genotyping or recent immunization history, see Recent immunization section) using one of the following methods:

• detection of measles virus RNA by PCR from an appropriate clinical specimen
• isolation of measles virus from an appropriate clinical specimen
• seroconversion or a significant (e.g. fourfold) rise in measles IgG titre by any standard serologic assay between acute and convalescent sera
• positive serologic test for measles IgM antibody using a recommended assay (see Laboratory comments section) in a person with clinical illness (see Clinical evidence section) who is either epidemiologically linked to a laboratory-confirmed case or is epidemiologically linked to a geographic area or community with known measles activity

Clinically-confirmed case

Clinical illness (see Clinical evidence section) in a person with an epidemiologic link to a laboratory-confirmed case.

Probable case

Clinical illness (in the absence of appropriate laboratory tests as well as the absence of an epidemiologic link to a laboratory-confirmed case) and one the following:

• In a person who is epidemiologically linked to a geographic area or community with known measles activity
• In a person with an epidemiologic link to a clinically-confirmed case (not laboratory-confirmed)

Laboratory comments

IgM serology has the potential for false-positive findings. If the clinical presentation is inconsistent with a diagnosis of measles or in the absence of recent travel/exposure history, IgM results must be confirmed by the other listed confirmatory methods.

Most acute measles cases develop IgM after 3 days post rash onset. Therefore, a suspected measles case in which serum collected < 3 days after rash onset initially tests IgM negative should have a second serum specimen collected > 3 days after onset for retesting for IgM.

Further strain characterization is indicated for epidemiologic, public health and control purposes.

For further details on laboratory diagnostics for measles, see Appendix F: Laboratory guidelines for the diagnosis of measles cases.

Clinical evidence

Usual clinical features of measles include all of the following:

• fever
• one or more of cough, coryza, or conjunctivitis
• generalized maculopapular rash

Clinical illness may present differently in breakthrough cases or cases who are immunocompromised, therefore clinician discretion may be required in applying clinical evidence. For further details, see Epidemiological characteristics of measles.

Recent immunization

Recent immunization with measles-containing vaccine can be distinguished from wild-type virus by genotyping or by specific PCR technology. In the absence of PCR diagnosis, vaccine history and clinical profile may be used to distinguish vaccine-strain. The most frequent reaction to measles-mumps-rubella (MMR) immunization is malaise and fever (with or without rash), usually occurring 6-23 days after immunization. However, this should be determined for each case, as these reactions and the time frame can vary (Canadian Immunization Guide).

ICD code(s)

• ICD-11 code(s)
  • 1F03
• ICD-10 code(s)
  • B05 Measles

Type of international reporting

Weekly reporting of confirmed cases to the Pan American Health Organization, in accordance with the 1994 goal of measles elimination from the Western Hemisphere.

References

Public Health Agency of Canada. Guidance for the public health management of measles cases, contacts and outbreaks in Canada. 2025.

Pan American Health Organization. Regional Framework for the monitoring and re-verification of measles, rubella, and congenital rubella syndrome elimination in the Americas. 2021.

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)

Guidelines for the Prevention and Control of Measles Outbreaks in Canada. CCDR 2013;39(ACS-3)