Surging measles cases in Southern Alberta have prompted health officials to abandon the use of public alerts to warn people of site-specific measles exposures.
Instead, Alberta Health Services, the provincial health authority, has issued a standing measles exposure advisory that warns anyone living in or visiting the South Zone that they are at “significant” risk of being exposed to the virus.
This standing advisory, which was released last Friday, replaced the use of alerts that warned the public about specific locations, such as businesses or clinics, where someone with a confirmed case of measles visited while infectious.
AHS said that site-specific advisories “no longer accurately capture the scope of potential risk at this time” in the South Zone, which covers the area south of Calgary and includes Lethbridge and Medicine Hat.
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“AHS continues to manage a significant number of cases of measles across the South Zone, including in individuals with no known exposure source,” the advisory said. “This indicates under-reporting of measles disease to AHS and a widespread potential exposure risk across all communities.”
The South Zone is the hardest-hit area in Alberta for measles with 452 confirmed cases, as of Monday. This represents 75 per cent of the province’s total caseload of 606, as of Monday. The majority of cases are among unvaccinated Albertans under the age of 18.
Alberta is at the forefront of Canada’s measles outbreak, second only to Ontario, which has logged roughly 1,800 cases. The disease’s domestic return has caught many physicians off guard as it was declared eliminated in Canada in 1998. One of the difficulties in containing measles is that it can live in the air for up to two hours after an infected person has left.
AHS is urging people to ensure their immunizations are up-to-date as the highly contagious virus snakes through the South Zone. Anyone who was born in or after 1970 and has fewer than two documented doses of the measles-mumps-rubella (MMR) vaccine is at risk, the authority noted.
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Lynora Saxinger, an infectious-diseases specialist at the University of Alberta, said the blanket advisory is concerning as it indicates that cases and exposures are multiplying at such a rate that they may no longer be possible to track.
“Outbreak control involves contact tracing and trying to get people to quarantine themselves if they’ve been exposed. So, that seems like a bad sign if it’s gotten to the point where that’s not really feasible,” Dr. Saxinger said.
“It really behooves people to not rely on exposure history and just go ahead and get their immunity tuned up if needed.”
She noted that people who are immunocompromised and unable to get immunized against measles, or too young to receive the measles-containing vaccine, are at high risk. Dr. Saxinger said she recommends that these individuals consider avoiding public spaces.
“Be choosy about where you go and how many people you expose yourself to during this period of time, especially babies,” she said.
While the first dose of MMR vaccine is typically recommended at one year of age, infants who are between six and 11 months can receive an early dose of vaccine if they live in or visit the South Zone. Two doses are still recommended after their first birthday.
