Two Sydney doctors with the coronavirus went to a conference that was attended by 77 medical practitioners and professionals.
A 53-year-old male doctor working at Ryde Hospital in Australia and a female doctor working at Liverpool Hospital attended the gathering on February 18.
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"We have had tracing going on," NSW Health Minister Brad Hazzard told reporters. "This is a bit like a police investigation in a sense, trying to track who is coming into contact with who and what possible associations there may have been.
"But what we do know is that the 53-year-old doctor, who was working at Ryde, was in attendance at that conference."
Forty staff members who work closely with the doctor at Ryde Hospital have been isolated. They include 13 doctors, 23 nurses and four other health workers.
"New South Wales Health has been working very hard to try to contact each of those doctors and other attendees of the conference. So far it has been positive, nobody else showing any symptoms of coronavirus."
The infected doctor is in a stable condition at Westmead Hospital.
Hazzard said there was an "evolution" happening in the spread of coronavirus around the world.
While there had been "no substantial change" overnight, seven of New South Wales' infections appeared to have been "on-soil," he said. There are currently 22 infections in the state.
The female doctor working at Liverpool Hospital is among six new confirmed cases of coronavirus in Sydney.
NSW's chief health officer Dr Kerry Chant said the female doctor was diagnosed on March 4 and had no history of overseas travel.
"We are immediately establishing which staff and patients may need to self-isolate and be tested for COVID-19 should they be unwell," she said.
This comes after a 95-year-old woman became the second person to die from the coronavirus in Australia, with seven more cases confirmed nationally.
The woman was a resident at the Dorothy Henderson Lodge nursing home facility at Macquarie Park, where a 50-year-old worker was diagnosed with the virus earlier this week, NSW Health confirmed in a statement. The woman died in hospital on Tuesday.
The employee worked with 13 residents at the lodge. An 82-year-old man is now being treated in hospital for the virus, while a third resident aged in her 70s was also diagnosed on Wednesday.
Eleven of the residents have been placed into isolation.
The Australian reports that staff at the home have collectively called in sick because of fears over the outbreak.
Hazzard told the newspaper his department was forced to make a snap decision and cobble together a workforce of nursing staff to care for the elderly residents once it was clear existing staff wouldn't be turning up.
Baptist Care said the death of a Dorothy Henderson Lodge resident "under these circumstances is very distressing" for the family and team members.
"Our staff have shown great dedication in the past days in their commitment to care for our residents and we continue to bolster our regular teams on the ground with additional specialist support from other locations across the state. NSW Health also has a team of experts guiding the response at Macquarie Park," she said.
"Working together, we have taken a firm approach to ensure any staff identified as being at risk are isolated and we have taken the added precaution of confining residents to their rooms across the centre. The NSW Health Infection Control team are also working with our team on the ground to provide additional support and reduce the risk of further exposure."
The five other new cases in NSW include a female patient from the Northern Beaches, a male from Cronulla and a female who is believed to have returned from the Philippines, NSW Health said.
There was also the first confirmed case in the Northern Territory.
It brings the state's total number of cases to 22 and the national count in Australia to 50.
The woman who is believed to have travelled from the Philippines is aged in her 60s and arrived back in Australia on March 3.
"Her travel details are being obtained and will be disclosed if she posed a risk to any other passengers on her flight," NSW Health said.
Addressing the nursing home cases on Wednesday, Hazzard said the carer was working on February 24 when she started developing flu-like symptoms.
"And so we did the checks. And, of course, we're aware that it's likely that she could have been capable of passing on the coronavirus from at least the day before, 24 hours, so that's 23 February," he said.
He said the woman was a "much-loved" and longstanding member of staff at a residential care home which is part of Baptist Care.
"It is concerning when we have somebody present with coronavirus and we can't track the source," Hazzard said.
"In this case, this much-loved staff member had not travelled. She had not been overseas. She had not been to any of the hot spots around the world. So, that raises the question, how did she end up with coronavirus?"