BARRIE, ONT. -- The number of COVID-19 cases in Simcoe Muskoka hit double digits on Monday.

There are 13 new cases of COVID-19, 11 Barrie residents under the age of 34, a Huntsville senior, and an Innisfil woman 35 to 44.

Barrie Mayor Jeff Lehman said the increasing cases are preventable. "It's social gatherings. It's not necessarily related to the business reopening.

What they are seeing is people contracting this from one another because they're not distancing, they're going to parties, nobody is wearing a mask, people are too close together inside for a long period of time," Lehman said.

There are currently 48 active confirmed cases in the region, and while hospitalization and death rates have slowed since June, testing for the virus has more than doubled in that time.

Health experts say it's only a matter of time before cases arise in schools now that thousands of students are back in class.

However, Simcoe Muskoka District Health Unit's Associate Medical Officer of Health, Dr. Lisa Simon, said it would take widespread transmission among students and staff before health officials closed a school.

"For example, if there were multiple classes where there were one or more cases, and it wasn't clear that the situation could be contained just by managing the situation in one class or another, there may be the need to shut down an entire school to break those chains of transmission," explained Dr. Simon.

Dr. Simon said the health unit doesn't foresee this occurring; instead, she believes it is more likely that "we will see a few cases here and there."

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Meanwhile, the province reports two more schools, for a total of 15, have cases of COVID-19 after one student and one staff member tested positive on Monday. There are no cases of COVID-19 reported in Simcoe Muskoka schools.

Ontario is reporting the highest number of new COVID-19 cases in 14 weeks with 313 diagnoses today. The province also recorded one new virus-related death on Monday.

In a news conference Monday afternoon, Premier Doug Ford said the surge in cases is "cause for concern."

Ford said more regional lockdowns could be coming, along with the second wave of COVID-19.

The premier begged Ontarians to be vigilant, saying, "It's within our grasp if we just follow protocols."

Ford urged people to continue to follow public health guidelines to slow the spread of the virus.

He said social gatherings where people don't respect those guidelines continue to be a main source of infection.

Health Minister Christine Elliott said that nearly 80 per cent of Ontario's cases are from three regions, Toronto, Peel and Ottawa.

Elliott said that almost 70 per cent of today's cases are in people under 40.

- With files from The Canadian Press