Thousands of people smiled, laughed, shook hands and conversed at one of the largest dental conferences in North America last month unaware of a deadly virus circling among them.

More than 15,000 attendees, presenters or vendors were part of the Pacific Dental Conference at the Vancouver Convention Centre in early March. Six days later, public health officials sent out a warning: an attendee had tested positive for COVID-19.

More positive tests followed. A dentist from British Columbia, Dr. Denis Vincent, died two weeks after the convention.

In the days and weeks that followed, positive cases linked to the conference popped up across Canada: at least 32 in B.C., nine in Alberta and three in Saskatchewan.

It's not known how many people were infected with the novel coronavirus at the convention because not all regions have provided that information.

Ontario let dental-care partners know of the potential risk, but has not revealed publicly how many cases have been traced back to the event.

Quebec says it doesn't appear that many of its positive tests are linked.

Nova Scotia and Prince Edward Island say no cases there go back to the conference.

Manitoba hasn't revealed any possible connections either. Although the first death in the province from COVID-19 was a woman in her 60s who worked for a dental supply company. That company had a booth at the Vancouver conference. The company directed The Canadian Press to speak with provincial health officials.

Some attendees may have contracted the virus but never showed symptoms.

“(Infectious diseases) are unpredictable,” says Jason Kindrachuk, a research chair in emerging viruses at the University of Manitoba.

Kindrachuk says public health officials made decisions based on the information they had early on. There were “unfortunate misnomers:” believing the virus only affected seniors or people with underlying health conditions, and that only those showing symptoms could spread it.

We now know a lot more people can be at risk and can unknowingly be carriers, Kindrachuk says.

The situation across Canada has been changing daily as positive COVID-19 test results continue to rise. Some of those cases have been linked to other super-spreading events.

More than 50 doctors from Western Canada were at a curling bonspiel March 11-14 in Edmonton, where an individual unknowingly spread the virus after returning from a trip to Las Vegas, said Alberta's chief medical health officer. Attendees from multiple provinces have since tested positive. At the time, events with less than 250 people could go ahead.

A snowmobile rally where more than 100 people gathered for supper in Saskatchewan on March 14 has been connected to nearly 20 cases.

And more than 100 positive cases, including one death, have been linked to funeral services in St. John's, N.L.

Across the country, as more information came in, large-scale events were cancelled, then smaller events. Then it was recommended people only be around those they live with. Recommendations from health officials and politicians became orders.

Alyson Kelvin is an assistant professor at Toronto's Dalhousie University and a research scientist at the Canadian Centre for Vaccinology. She says we're still in the early stages of understanding COVID-19.

Just a few weeks ago, there wasn't much evidence of community transmission in Canada. Scientists are now learning how long the virus survives on different surfaces and how easily it can be spread even at small events.

“There's a big difference between a couple of weeks ago and now,” Kelvin says.

Our understanding of how it is shared by children is also changing. Kelvin studied research out of China that traced children in households where people had tested positive. It showed that many children had contracted the virus but weren't showing any symptoms.

“This trend could continue in Canada or the U.S., where we have children being able to be infected and spread or transmit the virus and not even know that they had it.”

Normal life may seem like ages ago, Kelvin adds, but efforts to slow down the pandemic's spread are just beginning. And super-spreading events show just how important it is to keep social distancing.

“I know Canadians can do it because we have a great sense of our community in our country. Even though we are spread out, I know that we can come together by staying apart.”

This report by The Canadian Press was first published April 2, 2020