A Canberra Hospital ward has been declared a red zone and locked down after two patients tested positive for COVID.
Canberra Health Services chief executive Dave Peffer on Saturday confirmed the cases.
Mr Peffer said a person presented to hospital on September 18 for a procedure while they unknowingly had COVID.
The patient shared a room with another person with positive test results for both returning only yesterday.
"We are looking at an evolving situation. Our infectious diseases team has responded very rapidly," Mr Peffer said.
He said the team had conducted a thorough risk assessment of the situation in ward 10A and both patients have been moved to the hospital's established COVID ward.
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"Patients and our team members are currently undergoing testing at the moment," Mr Peffer said.
"No patient will be discharged from that ward until we have confirmed test results back.
"Any staff member that had worked or consulted on ward 10A since September 18th, we're contacting to be tested as well."
Mr Peffer said contact tracing had begun, including among support workers, as soon as the cases were identified, saying "there's some very busy phone calls at the moment to trace who have moved through that area".
"We're working with public health to investigate how long these patients have been infectious," he said.
Mr Peffer said evidence suggested the initial patient contracted the virus outside the hospital after presenting "for reasons unrelated to the virus" and had "no clinical indication that they were carrying the virus".
"Enhanced infection prevention control measures have been introduced to minimise any further spread," he said.
"This sort of incident is not new. This has now occurred more than 20 times in our healthcare facilities and we are prepared for it.
"We have an expert infection prevention control team who is rapidly deployed to respond to these sorts of situations."
Mr Peffer said authorities were still investigating details of the patients, including their vaccination statuses.
"If individuals are unknowingly positive and moving about the community, that's where we can see some of these challenges," he said.
"The team responded as quickly as they could."
Mr Peffer said visitors may still attend the hospital.
Ward 10A was designated as a green zone for surgery and consultation before the COVID cases.
The ACT recorded 32 new cases overnight, bringing the total to 233 active cases.
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