Public Health Alert

To: Ottawa Physicians and Nurse Practitioners

Date: April 28, 2025

From: Dr. Michelle Foote, Associate Medical Officer of Health

Subject: Measles updates and reminders: epidemiology, suspect cases, and vaccination

Dear Colleagues,

Measles outbreak activity continues in some regions of Ontario. This alert provides an update on the current epidemiology of the outbreak, an overview of steps to take if you suspect measles in a patient, and a summary of provincial vaccine recommendations.

Epidemiology of the multi-jurisdictional outbreak:

Measles activity continues in some regions of Ontario as part of the multi-jurisdictional outbreak. Public Health Ontario (PHO) produces a weekly Enhanced Epidemiological Summary related to measles in Ontario.

In 2025 (as of April 23^rd) a total of 1,018 measles cases (908 confirmed, 110 probable) have been reported in Ontario. Of these cases, all but 35 cases have been linked with the ongoing multi-jurisdictional outbreak. Nine cases had a history of travel (i.e. measles acquired outside of Canada) and one case was epidemiologically-linked to a visitor to Ontario; 25 cases do not yet have a source of exposure reported.

The weekly increase in case numbers has fluctuated around 100 for the past several weeks, and is due to continued exposures and transmission among individuals who have not been immunized. The highest number of cases has occurred in southwestern Ontario, with some localized areas affected in southeastern and northeastern Ontario.

The majority of cases associated with this outbreak have been infants, children and adolescents (75%), 95% of whom were unimmunized. To date, 76 individuals have required hospitalization. As of April 28^th, there have been no confirmed cases of measles among residents of Ottawa. PHO maintains a list of Measles Exposures in Ontario, which is updated each Tuesday and Friday to include exposures listed in public advisories issued by public health units.

If measles is suspected in a patient:

1. Provide the patient with a medical mask and place them in a negative pressure room.

• In the absence of a negative pressure room, place the patient in a single patient room with the door closed. The door must stay closed, and the room must not be used for 2 hours after the patient leaves the room.

2. Obtain specimens for STAT testing:

• NP swab or throat swab, AND urine for measles PCR
• Diagnostic serology (Measles IgM and IgG) can be considered but is not required. Collection of samples for PCR testing is the most important component for diagnosing measles.

3. Contact Ottawa Public Health immediately to report the suspect case:

• Notify OPH at 613-580-2424 ext. 24224 from Monday to Friday 8:30 am to 4:30 pm or dial 3-1-1 after hours and ask for the Public Health manager on-call.
• Reporting a suspect measles case should not be delayed pending lab results.

4. Instruct the patient to isolate at home while results are pending.

Measles typically presents with fever followed by a maculopapular rash that begins on the face. Prodromal symptoms can include cough, conjunctivitis, coryza, and possibly Koplik’s spots (small white spots on the inside of the mouth and throat). The characteristic maculopapular rash starts on the face and spreads down the body and usually begins 3 to 7 days following the prodrome.

Contrary to prior practice, it is no longer expected that providers speak with an Infectious Diseases provider prior to sending measles testing (throat/NP swab and urine) from their offices. Patients with suspected measles should not be directed to a hospital emergency department or hospital laboratory for any measles work-up, including serologies. The CHEO Infectious Diseases team is available for referrals for pediatric patients needing clinical evaluation (not testing alone) and to discuss whether testing is indicated for a more complex patient situation where exposure history and/or signs and symptoms do not clearly indicate testing. Providers wishing to consult with the CHEO Infectious Diseases team should call 613-737-7600 x0 and ask for the Infectious Diseases physician on call. To minimize exposure, DO NOT send a child you suspect has measles to any health care facility without prior notification.

See the OPH Public Health Alert posted on February 12^th, Measles Update and Resources for Health Care Providers, for details and additional resources on the clinical presentation, assessment, testing, and management of those suspected of having measles. You can also visit OPH’s Measles website for health care providers, which is currently under review to reflect the ongoing outbreak.

Measles vaccination

Measles-containing vaccines (MMR or MMRV) are part of Ontario's routine immunization schedule. Two doses provide very high levels of protection and immunity is usually lifelong.

• The Ontario Routine Immunization Schedule recommends two-doses of a measles-containing vaccine be given to children, given at least 28 days apart, after 12 months of age and again at 4 to 6 years of age.
• Where possible, the second dose of measles containing vaccine (MMRV) should be given closer to age 4 than age 6 years.

High Risk Eligibility Criteria (Table 3 of Ontario's Publicly Funded Immunization Schedule) include:

• If a child is travelling to areas where measles is circulating, an initial dose of MMR vaccine can be given as early as 6 months, however, 2 additional doses of a measles-containing vaccine given at least 28 days apart must be administered after the child is 12 months old to ensure long lasting immunity to measles.
• If a child is travelling to areas where measles is circulating, consider giving a second dose of measles containing vaccine earlier than age 4-6 years. MMR should be given, if the dose is given prior to 4 years of age. The child will require varicella vaccine at age 4.
• Ideally, give measles vaccine at least two weeks before travel. A minimum interval of 28 days is required between the first and second dose.

The priority for measles vaccination continues to be children at 12 months of age receiving their first dose, and again at 4-6 years of age for the second dose.

• Measles immunization should be guided by records of previous doses of measles-containing vaccines. As per the Canadian Immunization Guide, if a patient’s immunization records are unavailable, ordering serology to determine immune status is NOT recommended. It is safest to assume the individual did not receive the vaccine and proceed with immunization with a measles-containing vaccine. (Note: specific occupational groups such as health care workers may require serology for employment purposes).