TORONTO — About 1,000 people who attended a Christian youth event in Toronto earlier this month are being warned they may have been exposed to measles as the number of confirmed cases in Ontario continues to rise.

The province’s acting chief medical officer is asking people who were at the “Acquire the Fire” gathering held at the Queensway Cathedral on Feb. 6 and 7 to check their immunization status after it was confirmed a participant had the disease.

Organizers say roughly 1,000 people were present for the 27-hour event, described on the company’s website as “the weekend that changes your teen’s life forever.”

Health officials say participants, as well as performers and volunteers, came from all over Ontario.

Individuals born after 1970 who were at the gathering are being asked to review their immunization status to ensure they are protected against measles.

The majority of teens in Ontario have received two doses of the measles vaccine, and for most, that is “highly effective” at preventing the illness, the province said.

Measles symptoms begin seven to 18 days after exposure, and the virus is most often spread before people realize they have it, according to the Public Health Agency of Canada.

Those who took part in the event and develop symptoms of fever, cough, runny nose, inflammation of the eyes or rash over the next two weeks are being advised to phone their doctors.

The warning came as four new cases of measles were confirmed Monday in the province — one in Toronto and three in the Niagara Region, for a total of 15 so far.

The Toronto case — a child whose vaccine history is unknown — is not connected to the youth gathering, Toronto Public Health said in an email.

Officials in the Niagara Region would only say that the three new cases were linked to two earlier confirmed cases.

They urged people who attended Our Lady of Mount Carmel elementary school on Feb. 9 and 10 or Saint Michael high school between Feb. 6 and 10 to review their immunization records. Both schools are in Niagara Falls.

Health officials in Quebec confirmed on Wednesday that 10 individuals in the Lanaudiere region northeast of Montreal had been infected with measles, with all cases linked to the outbreak at Disneyland in California.

On Tuesday, the Manitoba government reported the province’s first case of measles of the year, a Winnipeg infant who had recently returned from India.