Western Australia's latest coronavirus outbreak within hotel quarantine remains unexplained as the state again recorded no new local cases.
Authorities are continuing to track down people who had contact with a hotel quarantine security guard and two of his housemates.
The trio tested positive on Saturday, prompting the government to reinstate mandatory mask-wearing both indoors and outdoors, close nightclubs and prevent fans from attending Sunday's AFL western derby at Optus Stadium.
Premier Mark McGowan on Monday said WA Health had so far identified 58 close contacts and 26 had tested negative.
The guard in his 20s worked at the Pan Pacific Hotel, where it's believed he contracted the virus from a returned traveller from the United States.
Mr McGowan said officials didn't know how the transmission had occurred but insisted it was not caused by ventilation issues which had been detected in other quarantine hotels, three of which will close in coming weeks.
"As you've seen in other states, sometimes you'll never know," he told reporters.
"It appears that there's no obvious reason why it spread from one of those passengers to the security guard."
Health Minister Roger Cook said the guard had been stationed near a lift and it was possible the virus had spread through surface contamination.
Genomic testing has indicated the guard has the same US variant of the virus as two returned travellers who were staying on the same floor.
The guests, one who had returned from the US and the other from Indonesia, had arrived on the same plane.
Authorities have reviewed CCTV footage and are yet to identify any concerns.
The guard, who worked at the Pan Pacific between April 24 and 26, has been moved to hotel quarantine along with his seven housemates.
On his days off work from April 27 to 30, he moved through the community going shopping, seeing friends and visiting Mirrabooka Mosque.
Restrictions had been in place in Perth and Peel, following a snap three-day lockdown, which appear to have reduced the risk of a wider outbreak.
The guard's two infected housemates each worked as delivery drivers and it emerged on Monday they had delivered food to more than 100 people.
Those people are considered casual contacts and are being advised to get tested.
But health advice suggested the risk of transmission was very low given the drivers were required to wear face masks and had minimal contact with customers.
Seventeen of the close contacts went to cooking classes on April 27 and 28 at the Perth College of Business and Technology which was also attended by one of the housemates.
All close contacts are required to quarantine for 14 days.
Mr McGowan and Health Minister Roger Cook on Monday each received their first doses of the AstraZeneca vaccine.
They are part of the over-50s cohort who are now eligible to receive their jabs at one of several mass vaccination clinics across Perth.
Over-50s can get vaccinated by their GPs from May 17.
"I didn't feel a thing. It wasn't a difficult experience," Mr McGowan said.
"I would encourage everyone to go and get vaccinated when your time comes."
Australian Associated Press