Ontario health officials have confirmed a new case of COVID-19, the disease caused by the novel coronavirus, the fourth in the province since the global outbreak began late last year.

Dr. David Williams, Ontario's chief medical officer of health, Dr. Barbara Yaffe, Ontario's associate chief medical officer of health, and Dr. Eileen de Villa, Toronto's medical officer of health, spoke to media at Queen's Park following word of a new presumptive case over the weekend.

De Villa said during the news conference that a woman in her 20s arrived in Canada from China on Friday and went to North York General Hospital in Toronto with an intermittent cough. She had travelled to the epicentre of the virus in January.

"In that travel to China, we know it did include some travel to Hubei province and to Wuhan in particular," she said, referring to the Chinese province and city where the virus first emerged late last year.

De Villa said the woman was tested for the new virus and was sent home for self-isolation because her symptoms were "resolving" and she was doing "quite well."

Officials said the woman's local tests came back positive for the virus on Sunday.

A sample was sent to the National Microbiology Lab in Winnipeg and, after Monday's news conference ended, officials learned that it came back positive.

Patient has had 'very, very limited exposure to others'

Since arriving in Toronto, de Villa said the woman has had "very, very limited exposure to others."

"Our staff at Toronto Public Health [is] following up directly to connect with this individual on a very regular basis and we are monitoring her symptoms," she said.

De Villa said they will be monitoring a family member who drove the infected individual from the airport to her home. The family member was wearing a mask during their interaction, Williams said.

Officials said the province is co-ordinating with local public health units to ensure that they will contact and monitor passengers who sat close to the woman on the plane.

De Villa said the current research advises the agency follow up with people who sat up to two seats away in all directions from the infected individual.

System to manage spread of virus 'working'

This is the province's fourth case and the third in Toronto, however health officials said the process put in place to manage the spread of the virus is working well.

"The whole process that has been followed from start to finish here shows that, in fact, the system is working quite well to keep people safe," de Villa said.

She said the patient was able to identify her symptoms and travel history to officials, staff followed the appropriate precautions and the patient wore a mask and limited her exposure to others.

"At this time, the risk here in Toronto continues to be low," she said.

On top of the three resolved cases and the most recent positive case, Yaffe said nine cases are still under investigation in Ontario and there have been 540 negative tests.

Ontario's first three cases 'resolved'

According to the province, Ontario's first three cases of the new coronavirus are all "resolved," which means each of those patients has had two consecutive negative tests at least 24 hours apart.

Three people in Ontario had previously been diagnosed with COVID-19, including a married couple in Toronto and a Western University student in London, Ont., after all of them recently returned from travelling in China.