Two food delivery drivers could have been infectious when they delivered food to homes over several days before testing positive to coronavirus.
The individuals were housemates of a hotel quarantine security guard and could have been positive for the virus as early as April 27 before working on April 29 and 30.
"Public health advice is that the risk is low when it comes to food deliveries, given the minimal contact and the requirement to wear masks," Western Australia's Premier Mark McGowan said on Sunday.
"Contact tracing teams are working through the restaurants they attended for short periods to pick up food and also delivery points."
Mr McGowan said there were no new cases linked to the outbreak after announcing three cases on Saturday.
He added the risk was low given the nature of food delivery work typically being low contact, as well as the community "being in a state of semi-lockdown" during the period they were potentially infectious.
One of the food delivery workers also attended cooking classes at the Perth College of Business and Technology on April 27 and 28, Mr McGowan said.
"Currently we understand about 20 people were also in that class and they have been contact or are being contacted as we speak, so they can be tested and put into isolation," he told reporters.
"The cooking class mates have not been included in the close or casual contact numbers listed earlier but they will be added once they have been identified by health experts."
Results are pending for a further four close contacts, while another 136 contacts are deemed casual or yet to be classified.
All the new cases and their close contacts must quarantine for 14 days.
The premier said he would not place the state into another lockdown, and instead revealed masks would still be required by those in the city and the Peel region.
He also announced there would be no spectators permitted at the AFL derby at Optus Stadium Sunday afternoon, saying it was "too much of a risk" to have them in attendance.
"The game will still go on and of course people can watch it from their own homes stop the decision to have no crowd at the stadium also helps us in preventing possible transmission on public transport," he said.
"Having 45,000 people try to get to Optus Stadium at the same time is too much of a risk, especially as we are still going through the close contacts."
Nightclubs will close for the next week and all Perth and Peel residents must wear masks indoors and outdoors, regardless of proximity to others.
Hotel guard returned positive result on Saturday
The guard in his 20s worked at the Pan Pacific Hotel between April 24 and 26 and tested positive on Saturday.
On his days off work from April 27 to 30, he moved through the community going shopping, seeing friends and visiting Mirrabooka Mosque.
He and his seven housemates were moved to hotel quarantine after he returned the positive result.
The guard had received his first dose of the Pfizer vaccine just days earlier.
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