Brittany Greeson/The Washington Post via Getty Images The Ambassador Bridge connecting Windsor, Ont. to Detroit is seen on June 28, 2018.

TORONTO — About half of Ontario’s newest cases of COVID-19 can be traced to travel to the United States, public health authorities said Monday. The news comes on the same day the federal government announced stricter border measures — that still allow American citizens to cross into Canada. “Basically, the numbers are going up very rapidly,” Dr. Barbara Yaffe, associate chief medical officer of health, told reporters at Queen’s Park. “We have found the numbers of new cases have almost doubled in a few days ... We have 32 new ones in the last 24 hours. And a significant number of those were exposed [to the virus] in the United States.” Ten of the 32 new cases are still being investigated, Yaffe said, so their cause is not yet confirmed.

I’m concerned about people coming from lots of places. Dr. Barbara Yaffe

Public health officials are conducting detailed interviews with every individual diagnosed with COVID-19 to trace their activities and all the people they came into contact with during the two weeks prior to their diagnosis, she said. Yaffe added that she is worried about travellers arriving from the U.S. still being allowed to enter Canada. “I am concerned, obviously, about people coming from the States right now. But I’m concerned about people coming from Italy. I’m concerned about people coming from lots of places.” Earlier Monday, Prime Minister Justin Trudeau announced Canada is closing the border to most non-residents, but he said U.S. citizens would be exempted, for now. Watch the prime minister’s announcement. Story continues after video.