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Reporting Obligations

Individuals who have or may have measles shall be reported to the local Health Unit.

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Aetiologic Agent

Measles is caused by the measles virus, a member of the genus Morbillivirus of the family Paramyxoviridae.

Clinical Presentation

Symptoms of measles begin 7–21 days after exposure to a case of measles and include fever, runny nose, cough, drowsiness, irritability and red eyes (conjunctivitis). Small white spots (known as “Koplik’s spots”) appear on the inside of the mouth and throat. Then, 3–7 days after the start of the symptoms a red, blotchy (maculopapular) rash appears on the face and then progresses down the body. Complications include diarrhea, pneumonia, blindness, otitis media and encephalitis.

Modes of Transmission

The virus is highly contagious and is spread by airborne droplet nuclei, close personal contact or direct contact with the respiratory secretions of a case. Transmission can occur as a result of the persistence of the virus in the air or on environmental surfaces. Measles virus can remain active and contagious in the air or on infected surfaces for at least two hours. Measles is one of the most highly communicable infectious diseases.

Incubation Period

About 10 days, but may be 7–21 days from exposure to onset of fever, usually 14 days until rash appears.

Period of Communicability

One day before the start of prodromal period, which is usually about 4 days before rash onset, to 4 days after the onset of rash.

Risk Factors/Susceptibility

Contact with case.


Not immunized or partially immunized.


After infection, immunity is generally lifelong. The following individuals should be considered susceptible: lack of documented evidence of vaccination with measles-containing vaccine (age dependent) or lack of laboratory evidence of prior measles infection or lack of immunity.

Diagnosis and Laboratory Testing

Lab confirmation of infection with clinically compatible signs and symptoms in the absence of recent immunization with measles-containing vaccine. Clinically compatible signs and symptoms are characterized by all of the following: fever ≥ 38.3 degrees Celsius (oral) and cough, coryza or conjunctivitis followed by generalized maculopapular rash for at least three days.

Laboratory diagnosis of measles should include both diagnostic serology and virus detection. See Labstract for more details.

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Treatment and Case Management

There is no specific treatment for persons with measles infection; however severe complications can be avoided through supportive care that ensures good nutrition and adequate fluid intake. Individuals diagnosed with measles should be advised to stay home for 4 days after the appearance of the rash. Self-isolation will help to prevent further transmission of the virus.

A measles contact is any susceptible person who shared the same air space for any length of time during the period of communicability, including two hours after the case left the air space (e.g. home, school, day care, school bus, doctor’s office, emergency room, etc.).

The timely administration of MMR vaccine or immune globulin (Ig) can be used to reduce the risk of infection in susceptible individuals exposed to measles. Post-exposure prophylaxis (PEP) is not 100% effective and contacts who receive PEP should be counseled on the signs and symptoms of measles and to avoid contact with high risk individuals.

Further information regarding Post-Exposure Prophylaxis (PEP) recommendations with MMR vaccine or use and dosing of Ig can be found in the Canadian Immunization Guide for Measles or the GamaSTAN®S/D product monograph.

*Also, please refer to the Reference listed below for more detail about the administration of PEP and exclusion of susceptible contacts.

Individuals that refuse or cannot receive MMR vaccine or Ig may be excluded from licensed child care settings, schools, and post-secondary educational institutions at the discretion of the medical officer of health; and may be required to self-isolate from work places, or other group settings, including travel.

There is no requirement to exclude individuals for any length of time after their receipt of vaccine or Ig before their re-entry to childcare settings, schools, or other settings (with the exception of healthcare workers).

Public Health staff will be involved with contact identification and tracing, assessing susceptibility, PEP information, and exclusion decisions.

Patient Information

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Additional Resources

Test Information Index | Public Health Ontario

Public Health Agency of Canada. “Measles: Symptoms and Treatment.”

Publicly Funded Immunization Schedules for Ontario June 2022

Public Health Agency of Canada. “Canadian Immunization Guide, Measles Vaccine.”


Ministry of Health and Long-Term Care. Infectious Diseases Protocol, 2022.