National case definition: Measles

Date of last revision: May 2008
Date of last review: May 2008

National notification

Only confirmed cases of disease should be notified.

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

Confirmed case

Laboratory confirmation of infection in the absence of recent immunization (see Clinical evidence section) with measles-containing vaccine:

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

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.

Clinical evidence

The most frequent reaction to measles-mumps-rubella (MMR) immunization is malaise and fever (with or without rash) occurring 7-12 days after immunization. However, this should be determined for each case, as these reactions and the time frame can vary (Canadian Immunization Guide, 7th edition).

Clinical illness is characterized by all of the following features:

• fever of 38.3° C or greater
• cough, coryza or conjunctivitis
• generalized maculopapular rash for at least 3 days

ICD code(s)

• ICD-10 code(s)
  • B05 Measles
• ICD-9/ICD-9CM code(s)
  • 055 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.

Comments

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

The case definitions for measles provided in this document are for routine surveillance purposes. Readers are referred to the document Measles surveillance: guidelines for laboratory support for further information on laboratory issues and the role of laboratories and public health in sporadic cases and outbreaks.

References

Measles surveillance: guidelines for laboratory support. CCDR 1999;25(24).

Pan American Health Organization. Measles Elimination Field Guide. 2^nd edition. Scientific and Technical Publication No. 605. Retrieved May 2008.

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).