Ontario health officials confirmed a third person has tested positive for coronavirus, just hours after a Toronto hospital released the country's first patient with a confirmed case of the disease.

The newly confirmed patient is a woman in her 20s from London, Ont., the province said. She arrived in Canada on Jan. 23 from Wuhan, China.

The woman's case is different from Ontario's first two confirmed cases, health officials said, because she originally tested negative for coronavirus and was initially asymptomatic.

A second, more advanced test was later administered, which confirmed she was carrying lower levels of the virus in comparison to other patients with the disease.

The woman, who studies at Western University, made a full recovery within two to three days.

Dr. David Williams, Ontario's chief medical officer of health, said she is unlikely to have passed on the virus to others. The woman wore a surgical mask during her journey from Wuhan and put herself in self-isolation after arriving in London, only leaving her home to visit the hospital.

"There's been no risk at all to Ontarians," Williams said. "Returning travellers have been very responsible."

All possible cases are being retested as more information about the virus becomes available, said Dr. Vanessa Allen, chief of medical microbiology at the Public Health Ontario Laboratory.

"This is part of the science of the way that we develop rapid tests for a response to a new pathogen that we're just learning more about," she said.

No other patients have had their negative tests reversed. The cases are being retested by both provincial and national laboratories.

1st patient on 'clear trajectory of improvement'

The new confirmation comes after the patient with Canada's first confirmed case of coronavirus was discharged from a hospital in Toronto on Friday morning and returned home to stay in self-isolation.

The man was being treated at Sunnybrook Health Sciences Centre after arriving on a flight from China last week.

Doctors at the hospital said the man's condition improved during his stay and that he no longer requires in-patient care.

"We're not anticipating his condition to worsen," said Dr. Jerome Leis. "He seems to be on a clear trajectory of improvement."

The man was being held in a negative pressure room after being admitted to the hospital on Jan. 23, a day after returning from Guangzhou, China. Leis said the patient was offered "supportive treatment" such as fluids, oxygen and blood work since no direct treatment for the illness exists.

Dr. Jerome Leis said the patient mostly recovered on his own during his time at the hospital. (CBC)

The patient's wife also has a confirmed case of the virus, although she has been at their home in self-isolation. Public health officials said Thursday that she is "doing well" and hasn't shown symptoms of infection.

Sunnybrook said home-isolation now represents the man's best path to recovery while posing little risk to the general public. The couple will be monitored by Toronto Public Health while at home.

"We have seen that this condition can be successfully managed with home isolation in many other cases and we felt that was the best approach," Leis said.

Both patients are in their 50s, health officials said.

The couple visited Wuhan, the epicentre of the novel virus that has killed 213 people in China and sickened about 9,800 around the world.

Sunnybrook said the patient was not available to speak about his experience with the illness.

Risk to the public is 'zero,' doctor says

Ontario is investigating 17 possible cases of coronavirus in addition to the three confirmed cases, though public health officials say most of the patients are unlikely to be carrying the virus.

Dozens of other patients have already had their cases cleared.

Dr. Michael Gardam, chief of staff at Humber River Hospital, said there is no reason to believe the illness will begin spreading in Canada.

Dr. Michael Gardam, Chief of Staff at Humber River Hospital, talks about the spread of the virus, the medical and government responses, and says Toronto will continue the work to be one of the best prepared jurisdictions in the world. 7:31

"We don't have any evidence whatsoever, in any of the countries where this has been imported, that we're seeing spread into the general community," he told CBC Radio's Metro Morning on Friday.

"The risk right now, in Toronto or in Canada, for the general public ... is zero," he said.

On Wednesday, health officials confirmed that a man in his 40s, from the Vancouver area, is British Columbia's first case of coronavirus. He's in isolation at home after developing symptoms, following a business trip to Wuhan.