A sixth case of the measles was confirmed last week in Ontario's Niagara region. Officials believe it is connected to the other five and to a youth gathering in Toronto earlier this month.
There are now 17 confirmed cases in Ontario, as well as others across the country, and concerns about vaccinations are growing.
So far, health officials in Ontario say none of the cases has been linked to the outbreak of measles at Disneyland, even though several cases in Quebec have been connected to the California theme park.
Provincial officials say at least one of the Niagara patients had traveled to Toronto for a youth gathering called Acquire the Fire on February 6 and 7.
"Some of the cases are school age cases, so by the time you add up the number of students and connected schools and the teachers and clubs and church and all places, we have to trace probably close to 2,000 people," said Dr. Valerie Jaeger, the Niagara region medical health officer.
Jaeger says the latest case is a woman under 30 who was not vaccinated, and that has become an issue -- more and more people, children especially, who have not had their measles vaccines.
The federal health minister, Rona Ambrose, says some parents choose to ignore the science and not vaccinate their children.
"We have people that are refusing to vaccinate their children, putting them at risk. But most importantly, you're putting other children at risk," said Ambrose.
The Ontario health ministry is particularly concerned about the Acquire the Fire event in Toronto. It warns that as many as 1,300 people were exposed to measles during the two-day Christian youth event.