Open this photo in gallery Signs advise visitors to PDAC to help stop the spread of germs as they head down to the convention floor in Toronto on March 2, 2020. Fred Lum/the Globe and Mail

Ontario health officials are investigating how a man who attended a major conference in Toronto contracted COVID-19, fearing the case marks the start of local transmission of the virus in the province.

Public Health Sudbury and Districts, which posted details of the case online Tuesday evening, said a man in his 50s tested positive for COVID-19 after attending the Prospectors and Developers Association of Canada conference on March 2 and 3. According to organizers, the annual event attracts 25,000 attendees from more than 130 countries.

Anyone who attended the conference is now being asked to monitor themselves for symptoms such as a fever or cough for the next 14 days, according to Penny Sutcliffe, Sudbury’s medical officer of health.

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Mining industry pressing for more details on PDAC delegate with COVID-19

Prime Minister Justin Trudeau, Ontario Premier Doug Ford and a number of provincial and federal cabinet ministers and business leaders attended the conference.

It’s unclear how or when the man became infected with the virus. He could have been exposed to it by an international traveller at the conference. Regardless, the case likely signals that community transmission of the virus has begun in Ontario, said Lucas Castellani, an infectious-disease physician based in Sault Ste. Marie, Ont. Community transmission refers to local spread of the virus not linked to international travel.

“Overall, the implications are kind of the same,” Dr. Castellani said. “He would’ve gotten it or gotten in contact with someone who acquired it at the conference. By the time testing is done, he could have transmitted it to one or two other people now. It makes sense we’re further along in this community [transmission] chain than maybe we recognize.”

Sudbury officials say the man returned to work on March 5 and 6 before seeking medical attention on March 7.

Ontario Energy Minister Greg Rickford confirmed Wednesday that the man is an employee of Northern Development and Mines and that the Sudbury office has been shut down to prevent transmission of the virus among his colleagues.

Health officials declined to say how many individuals are being tested for the virus in the area.

Laurentian University in Sudbury announced Wednesday that all of its classes will be moved online as a preventative measure.

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Sumon Chakrabarti, an infectious-diseases specialist at Trillium Health Partners in Mississauga, said public health officials will be scrambling to determine who the Sudbury man came in contact with. The fact he likely contracted the virus at the conference also suggests that authorities and businesses should cancel large gatherings to reduce transmission, Dr. Chakrabarti said.

“I do think that we’re going to be seeing more and more of these [cancellations] in the coming days,” he said.

Dozens of people around the world have tested positive for COVID-19 after attending large conferences in recent weeks, including at the American Israel Public Affairs Committee conference in Washington, D.C., and last month’s RSA Conference in San Francisco. So far, 70 employees of biotechnology firm Biogen have tested positive for the virus after attending a company meeting in the Boston area.

B.C. officials confirmed Canada’s first case of community spread of COVID-19 last week in a woman who works in a long-term care facility. The province has since declared an outbreak at the facility, where one resident has died. The province has also confirmed several other cases of community spread.

Meanwhile, a physician at a Hamilton cancer centre has tested positive after returning from a trip abroad. The physician saw patients on the afternoon of March 9 at the Juravinski Cancer Centre, where she works as a radiation oncologist, before going to the emergency department of the Juravinksi Hospital to be tested.

The hospital said public health officials are now trying to contact all the patients she saw on March 9. In a news release, the hospital said the risk to those working in the hospital and those who had contact with the physician is low.

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Those who came in contact with her have been told to self-isolate at home for 14 days. It was not immediately clear how many physicians and nurses would be affected.

With files from Joe Friesen and Jeff Gray

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