Western Australia's COVID-19 testing blitz has again produced no new local or overseas cases, raising hopes the lockdown will end within days as scheduled.
But questions remain unanswered about the breach at the Sheraton Four Points quarantine hotel, including whether the security guard behind the outbreak was wearing a mask when he delivered medication to a sick guest.
He went on to roam the streets of Perth, attending more than a dozen venues over several days, while infected with the highly contagious UK strain.
A record 16,490 people were tested on Monday, the start of a five-day lockdown for metropolitan Perth, the Peel region and South West.
"This result on day one of lockdown is an amazing number," Premier Mark McGowan said on Tuesday.
"Thank you to everyone who came forward and got tested. You have all done your state proud."
Mr McGowan said he was encouraged by the early results but it was highly unlikely the lockdown would end ahead of schedule.
"My expectation is it will go the full five days," he said.
"I know that is debilitating and difficult ... I know a lot of people are suffering. But I just don't want to see a recurrence."
Contact tracers have now identified 151 close contacts and 68 casual contacts of the security guard, a man in his 20s dubbed "case 903".
All are being tested and 104 have so far returned negative results.
Genomic testing has linked the guard's case to the same UK variant present in two recently returned overseas travellers.
He is believed to have delivered medication to one of the travellers who was accommodated on the same floor on which he was working on January 24.
Pressed repeatedly, Health Minister Roger Cook was unable to say whether the guard had been wearing a mask.
"We haven't had the opportunity since getting that information, because it is quite fresh, (to investigate) the circumstances of that interaction," he said.
Mr Cook said hotel security guards were not expected to wear a mask at all times, even while on the same floor as confirmed COVID patients.
"If people are in their rooms and the guard is simply monitoring that corridor, not necessarily," he said.
"They would probably have to carry it with them in order to protect themselves in the event that someone left the room."
Mr Cook clarified that the guard had not reported being unwell to his employer until January 30 - two days after developing symptoms.
He was directed to get a COVID test and returned a positive result that night.
The man last worked at the hotel on the 27th but failed to isolate upon falling ill. He also attended a GP clinic in Nedlands on the 29th.
No further overseas arrivals will be sent to the Sheraton hotel until further notice.
Existing guests who were due for release in coming days will remain there until they return another negative test.
Anyone recently released from the hotel will also be contacted and required to self-isolate until they have again tested negative.
WA's health incident coordinator Robyn Lawrence on Tuesday claimed the guard "did everything right" and there was "no bungle" in the hotel quarantine system.
Police are continuing to investigate how the breach happened.
Anyone living in the lockdown zone, including school students, must stay at home unless shopping for essentials, attending to medical or healthcare needs, exercising within their neighbourhood or working if unable to do so remotely.
Metropolitan testing clinics are staying open until 10pm, but Opposition Leader Zak Kirkup has called for the government to open a 24-hour clinic.
He also wants an immediate end to some hotel workers holding second jobs.
Mr McGowan has said the government is close to enforcing such a ban which is likely to be softened by a 40 per cent pay increase.
The Sheraton guard is also a rideshare driver but is not believed to have worked in that job since January 22 - several days before likely becoming infected.
He is said to be fully cooperating with authorities.