The partner of the Brisbane cleaner who tested positive to the UK COVID-19 variant has also become infected but the city's lockdown won't be extended.
Chief Health Officer Dr Jeannette Young says the man has been in quarantine since January 7 and additional contact tracing is underway.
"We know this particular variant of COVID-19 is more contagious, so this result is unsurprising," she said.
"However it highlights the importance of why the Greater Brisbane lockdown was so important to ensure any potential spread of the virus is contained."
Genome sequencing is being conducted but it is likely to be the UK variant.
Additional testing of other close contacts of both the man and woman will continue this week.
There is no change to the restrictions which mark the conclusion of Greater Brisbane's lockdown.
Face masks were to remain mandatory but residents of Brisbane, Logan, Ipswich, Moreton Bay and Redlands allowed to leave home without reason from 6pm.
The three-day lockdown appears to have contained the highly contagious UK strain of COVID-19 with no new cases of community transmission reported since Friday.
"Can I thank people in the greater Brisbane region for responding in the way that they did? It has been absolutely, truly remarkable," Premier Annastacia Palaszczuk told reporters on Monday.
People must carry a face mask at all times for the net 10 days and wear them in indoor venues such as shops, hospitals, places of worship, libraries, cinemas, art galleries and gyms.
They are not required inside homes, restaurants or bars, or other places where people can socially-distance.
Dr Young says the lockdown allowed contact-tracers to find 370 close contacts of the cleaner.
She said 172 had already tested negative and the others were either getting tested or awaiting results.
Dr Young is still trying to find "less risky contacts" who visited three venues at the same time as the woman last week.
They include Woolworths at Calamvale North between 11am and 12pm on January 3, Coles Sunnybank Hills Shoppingtown between 7.30am and 8am on January 5 and a Sunnybank Hills newsagent between 8am and 8.15am on January 5.
"I'm not sure we've found everyone who attended those three venues yet," Dr Young said.
"So it's really important that anyone who has attended one of those three particular venues ... comes forward."
Chamber of Commerce and Industry Queensland's Amanda Rohan said the lockdown and the new rules were a setback for businesses during the crucial school holiday trading period.
She urged people to get out and support businesses while abiding by the new rules.
"What needs to happen now, is to know how we can prevent any future immediate shutdowns to avoid this uncertainty again," Ms Rohan said.
Opposition Leader David Crisafulli said the lockdown created uncertainty for business but it was a relief to see there were no new virus cases.
He said the police probe into the quarantine breach was crucial so that the overall system can be strengthened and future mistakes minimised.
Dr Young urged people to get tested, particularly in the Calamvale North and Algester areas, after 18,904 tests were conducted on Sunday.
Four new virus cases were reported in hotel quarantine on Monday - two Emirates crew members and two passengers who had arrived from the UAE.
Two of those people had travelled to the UK, but Dr Young said it was too early to know if they had the more contagious strain of the virus.
Australian Associated Press