Laboratory-confirmed:
Clinical illness1 and laboratory confirmation of measles infection in the absence of identification of measles vaccine strain based on PCR or genotyping^.
Laboratory confirmation may be determined by:
- Isolation of measles virus^ from an appropriate clinical specimen OR
- Detection of measles virus^ RNA by PCR from an appropriate clinical specimen OR
- Seroconversion or a significant (e.g., fourfold) rise in measles IgG titre by any standard serologic assay between acute and convalescent sera (collected 10-21 days apart) OR
- Positive serologic test for measles IgM antibody using a recommended assay* in a person who is either epidemiologically linked to a laboratory-confirmed case or a community or geographic area with known measles activity
^If measles vaccine strain is positive based on PCR or genotyping, then not a case.
*Confirmation of IgM results by PCR detection of the measles virus is recommended whenever possible, because false-positive IgM results may occur. If 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.
OR
Confirmed epi-linked:
Clinical illness1 in the absence of appropriate laboratory tests in a person who is epidemiologically linked to a laboratory-confirmed case.
Clinical illness1 in the absence of appropriate laboratory tests and in the absence of epidemiological linkage to a laboratory-confirmed case and at least one of the following:
- Epidemiological linkage to a community or geographic area with known measles activity
- Epidemiological linkage to a confirmed epi-linked case
Clinical illness1 in the absence of appropriate laboratory tests and with no clear epidemiological linkage to a lab-confirmed, confirmed epi-linked, or probable case or community/geographic area with known measles activity.
Laboratory detection of measles virus RNA by PCR‡ from an appropriate clinical specimen
AND at least one of the following:
- Specimen collected within the first 10 days of life
- Symptom onset1 within the first 10 days of life
AND at least one of the following:
- In a neonate whose mother/birthing parent was a confirmed or probable measles case
- In a neonate with no other suspected source of exposure to measles after birth
‡If an alternative method of laboratory confirmation was used (e.g., serological test for measles IgM antibody), the case should be assessed as a potential probable congenital measles case.
Clinical illness compatible with measles1 with symptom onset in the first 10 days of life, in the absence of appropriate laboratory tests
AND at least one of the following:
- In a neonate whose mother/birthing parent was a confirmed or probable measles case
- In a neonate with no other suspected source of exposure to measles after birth
Usual clinical illness is characterized by all of the following features:
- Fever
- Cough, coryza, or conjunctivitis
- Generalized maculopapular rash
Clinical illness may present differently in breakthrough cases or cases who are immunocompromised, therefore clinical discretion may be required in applying clinical evidence.
Definitions of epidemiological linkage
A case is considered to have an epidemiological linkage to another case if there was contact during one case's incubation period when the other case was infectious where measles transmission is plausible.
A case is considered to have an epidemiological linkage to a community/setting/geographic area with known measles activity (e.g., measles endemic or outbreak areas) if they had exposure (e.g., place of residence, travel) to the community/setting/area during their incubation period.
Please refer to section 3.0 of the Communicable Disease Control Manual, Chapter 1: Measles for definitions of measles incubation and infectious periods.
Date of last revision: September 2025
