Open this photo in gallery 'There are a range of estimates, but I would say that it is safe to assume that it could be between 30 per cent of the population that acquire COVID-19 and 70 per cent of the population,' Minister of Health Patty Hajdu, seen here, said in Ottawa. Adrian Wyld/The Canadian Press

Between 30 per cent and 70 per cent of Canadians could become infected with the new coronavirus that causes COVID-19, federal Health Minister Patty Hajdu said Wednesday, but that number will depend on the scope and scale of the response to combat transmission.

The COVID-19 outbreak is a “national emergency and crisis," Ms. Hajdu told the House of Commons health committee, but public health officials say they won’t prohibit mass gatherings until the virus spreads more widely.

“There are a range of estimates, but I would say that it is safe to assume that it could be between 30 per cent of the population that acquire COVID-19 and 70 per cent of the population,” she said.

Story continues below advertisement

While most will recover, she said Canadians must work together to protect seniors, people with underlying conditions and other vulnerable groups.

Coronavirus guide: The latest news on COVID-19 and the toll it’s taking around the world

I think I may have the new coronavirus. What should I do?

Calls for limits on public gatherings intensified Wednesday amid news a Sudbury man who attended a major Toronto conference held by the Prospectors and Developers Association of Canada tested positive for COVID-19. Unlike every other case identified in Ontario to this point, officials don’t know how or when the man became infected, but believe it was at the conference, meaning someone there was likely spreading the virus.

“What we are saying is that each case, it’s a case-by-case basis. It will depend on the kinds of risks in your community. It will depend on the number of cases in your community,” Ms. Hajdu told reporters Wednesday.

Ontario Health Minister Christine Elliott said the province had no immediate plans to bring in tougher measures, such as banning large gatherings, closing schools or putting students returning from travel in isolation – at least until cases that cannot be linked to international travel or visitors emerge.

“We’re not at that stage yet,” Ms. Elliott said. “… We’re watching this very, very closely.”

David Fisman, an epidemiologist at the University of Toronto’s Dalla Lana School of Public Health, said waiting to act before more cases pop up could put Canada in a situation similar to Italy, where the number of infections and deaths have spiralled out of control and forced the government to lock down the entire country.

Dr. Fisman said evidence shows countries that have adopted policies to keep people apart have been able to control the COVID-19 spread, while others, such as Iran, Italy and China, have faced massive outbreaks because of inaction.

Story continues below advertisement

“We have seen this play out,” Dr. Fisman said in an e-mail. “I am not sure why we need to reinvent the wheel.”

British epidemiologist Roy Anderson and colleagues wrote a commentary in the Lancet journal last week that highlighted how Singapore and Hong Kong, which both experienced the SARS epidemic in 2003, have done well this time despite their proximity and connections to mainland China.

Part of it comes down to swift action and clear messaging from authorities, Dr. Anderson said – but also to the fact that in both locations, people voluntarily and quickly changed their behaviour. He added that while governments must take the lead, “how individuals react to this is going to be more important. All of us have got to [keep our distance] … to try to flatten this epidemic.”

Bonnie Henry, B.C.'s Provincial Health Officer, said officials there are not ruling out anything, such as the cancellation of Easter church services or a delayed return to school after March break. It will all depend on what happens in the province in the next few weeks, she said.

“It’s not easy to say across the board everything should be cancelled because we want to continue with life as well,” Dr. Henry said.

Deena Hinshaw, Alberta’s Chief Medical Officer of Health, on Wednesday recommended all those who travel outside of Canada to limit their attendance at large public gatherings upon their return, and to self-monitor for symptoms. She said older people and people with underlying health conditions should think about the risks associated with mass gatherings, stopping short of advising against them.

Story continues below advertisement

The number of COVID-19 cases has increased dramatically in Canada in recent days, reaching more than 100 as of Wednesday. Those include the first cases on Vancouver Island and in New Brunswick.

Hamilton health officials said an oncologist tested positive for the virus after returning from a trip to Hawaii. The physician saw patients on the afternoon of March 9 at the Juravinski Cancer Centre before going to the emergency department to be tested. The hospital said public health officials are trying to contact all patients who were seen by the doctor.

The news that a man who attended the massive PDAC conference tested positive for the virus sent alarm bells across the country. Prime Minister Justin Trudeau, Ontario Premier Doug Ford and several political and business leaders were at the conference. Health officials say attendees should monitor themselves for symptoms for the next two weeks.

Ontario Energy Minister Greg Rickford confirmed Wednesday the man’s entire office in Sudbury has shut down. Laurentian University also announced it is immediately suspending all in-person classes and will hold them online for the foreseeable future.

Janine McCready, an infectious diseases physician at Toronto’s Michael Garron Hospital, said the man’s case is concerning because officials have no idea how many others were potentially exposed.

Mr. Ford said Wednesday the province had put $100-million aside for the health system to deal with COVID-19.

Story continues below advertisement

“We have a plan for every scenario,” said Mr. Ford, who is scheduled to meet his fellow premiers in Ottawa on Thursday and Friday. “As I think we all agree … this isn’t a time for politics. This is a time that we stick together as a province, we stick together as a country.”

Health Minister Patty Hajdu says the World Health Organization's declaration of a global COVID-19 pandemic doesn't change Canada's approach to fighting the virus. She says Canada has been preparing for the worst case scenario, and it will stay on its current course. The Canadian Press

With reports from Kristy Kirkup, Jeff Gray, Ivan Semeniuk, Joe Friesen and Andrea Woo

Our Morning Update and Evening Update newsletters are written by Globe editors, giving you a concise summary of the day’s most important headlines. Sign up today.