Concern is being raised that the Americas are entering a new phase of the coronavirus outbreak and that Toronto is only weeks away from the point where the illness begins to spread locally.

Ontario health officials confirmed three new cases of COVID-19, the disease caused by the novel coronavirus, on Saturday, the highest number of positives reported on a single day in the province.

The new cases include a 51-year-old woman who travelled to Iran, her 69-year-old husband, and a 34-year-old woman who also travelled to Iran. All are in self-isolation, as are the 34-year-old woman’s husband and young child.

Two of the cases were in Durham Region and the third in York Region. They are the first cases to be reported in both areas.

The news came a day after two other positive cases were reported in Ontario — one patient had travelled to Iran, the other to Egypt — bringing the overall total in the province to 11. Three of those patients have since recovered.

The fact that so many cases in Canada and other countries have been linked to Iran signals two important facts, according to Dr. Isaac Bogoch, an infectious disease specialist at the University of Toronto and Toronto General Hospital.

“If they’re exporting cases to Canada, Kuwait, Oman, Iraq, we know that the burden of illness in Iran is much larger than the numbers reported suggest,” said Bogoch, the co-author of a medical paper on the situation in Iran.

Bogoch said the rise in the number of countries exporting the virus and the fact that the illness is being spread locally in certain areas of the U.S. means that the Americas are entering a new phase of the outbreak, one in which the number of imported cases will likely climb, and locally acquired cases will begin to appear.

He estimated that the first locally transmitted cases could arise within several weeks. “This is part of the evolution of the epidemic,” he said.

The provincial Ministry of Health said on Saturday that Ontario is actively working with city and health officials to plan for the potential of local spread.

Toronto medical officer of health Dr. Eileen de Villa said Saturday afternoon that residents should not panic.

“The best available evidence says that this virus is not airborne; you have to have close contact with the respiratory excretions of an ill person,” de Villa told the Star.

“So, walking through the same Loblaws or Costco is not a significant exposure.”

Each case is carefully followed up, she said, and those who may have been in contact with a person known to be infected have been notified.

She said that the city is preparing for the possibility of local transmission. More testing is being conducted when people present flu-like symptoms in hospitals, or are admitted with respiratory problems.

“We’re asking people to stay up to date because we are regularly updating our information on our website and would really encourage people to rely on Toronto Public Health and other official, credible sources of information,” said de Villa.

The York Region case involved a patient at Mackenzie Health hospital in Richmond Hill.

After arriving in Toronto on Wednesday, the 34-year-old woman — who had travelled to Iran — went to the hospital the next day with a dry cough, runny nose, shortness of breath and headache.

She was wearing a mask on arrival at the hospital, a news release said.

“Due to the low severity of symptoms and the condition of the patient, the patient was not admitted to hospital,” the news release said. “The patient is in self-isolation, per protocols, where she remains.”

She developed symptoms prior to her return and was symptomatic on the flight, York Region said in a news release.

The woman flew with her husband to Toronto with a layover in Denmark. She wasn’t wearing a mask during her travels back home.

York officials urged all passengers who travelled in the business class section of Qatar Airways Flight QR483 and QR163 on Tuesday; who travelled in business class on Air Canada Flight AC883 on Wednesday; or who were sitting on the upper deck of GO bus No. 40 eastbound on Wednesday at about 3:55 p.m. to contact York Region Public Health, because they may have been exposed.

These people are asked to call 1-800-361-5653, Monday to Sunday between 8:30 a.m. and 8 p.m., for further assessment.

GO Transit posted a tweet Saturday saying that a person travelling on a bus from Pearson airport to Richmond Hill Centre was diagnosed with COVID-19. The transit agency said it was working with public health authorities to identify other passengers on the bus.

“It was only a matter of time before York saw a case of COVID-19,” Dr. Karim Kurji, the region’s medical officer of health, told reporters at a news conference.

Kurji said public health officials are trying to identify airline passengers who were seated within two rows of the patient.

The risk level on the GO bus is lower than on the plane because the period of travel was shorter, and there is a higher degree of ventilation and air movement on a bus.

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“We believe in aggressive contact followup. We have every confidence that we’ll be able to contain the exposure and we have isolated close to 600 individuals since the spread of the virus over the past few months,” Kurji said.

As of Saturday afternoon, fellow passengers hadn’t been contacted as officials did not yet have the flight manifests, Kurji said.

The woman’s husband and toddler are also in self-isolation, which involves separating members of the family: they cannot share the same room, washrooms, utensils or general living space. If they need to be in contact, they must be at least two metres away from each other, said Kurji.

“It’s quite difficult for a toddler who can’t see their mom,” Kurji said.

An internal hospital letter obtained by YorkRegion.com assured MacKenzie Health workers that all protocols had been followed.

“Because of the protocols in place, there were no staff, patient or visitor exposures related to this case,” read the letter written by Dr. Danny Chen, physician lead in infection prevention and control.

“Staff and patient safety will always remain a priority at MacKenzie Health.”

In Durham Region, two patients seen at Lakeridge Health Ajax Pickering also tested positive.

A 51-year-old woman returned to Toronto from Iran on Feb. 22. Six days later, on Friday, she went to an Ajax clinic while wearing a mask, with symptoms that included a cough, body aches and chill.

Her 69-year-old husband, who had a cough but did not travel with his wife to Iran, also tested positive for COVID-19 after bringing her to the clinic. Both husband and wife were discharged and put in self-isolation at home.

On Friday, Ontario health officials reported that a man in his 50s who had travelled to Iran had tested positive for the virus in Toronto. Later Friday night, officials reported that a Toronto man in his 80s with a travel history to Egypt had also tested positive.

Meanwhile, the British Columbia government has confirmed a case in the Vancouver Coastal Health region.

Provincial health officer Dr. Bonnie Henry said the eighth case in the province is a woman in her 60s from Tehran, Iran, who travelled to B.C. to visit family and developed symptoms a few days after arriving.

As of Saturday there were a total of 19 confirmed cases of COVID-19 in the country, plus one presumed positive case in Quebec.

Iran’s Health Ministry said Saturday that there were 593 cases in the country, with 43 deaths.

But last week the Star reported that the true number of coronavirus cases in Iran may be upwards of 18,000, according to a preliminary analysis by Canadian researchers.

“It’s a raging epidemic (in Iran) and the Iranian government appears to be in a state of denial,” University of Toronto epidemiologist Dr. David Fisman told the Star.

Experts have expressed concern that the extent of the outbreak in Iran is under-reported, and that uncontrolled transmission in the country could have profound consequences for limiting the global spread of the disease.

More than 85,000 people worldwide have contracted the virus, with deaths topping 2,900.

With files from Raneem Alozzi, YorkRegion.com and Star wire services