Mystery COVID-19 case cause still unknown - Dr Ashley Bloomfield

Director-General of Health Dr Ashley Bloomfield says it's still unknown how New Zealand's mystery COVID-19 case became infected.

On Sunday the Ministry of Health said two community cases of COVID-19 were linked to a confirmed case on Saturday - a recent returnee who completed two weeks of managed isolation and was allowed to leave after returning two negative tests.

He then flew home to Auckland on September 11. But the man developed symptoms five days later and tested positive. He's not linked to the existing Auckland cluster.

Addressing the situation on Monday, Dr Bloomfield says how the man became infected is "still under investigation" and "we are keeping an open mind".

He presents a range of scenarios - adding the Ministry of Health is "not ruling out any possibilities". These include:

Infected in India

"He could have been infected in India before departing and had a very long and unusual period of incubating the virus - that is rare but it can happen," Dr Bloomfield says.

Infected on flight to NZ

"He could have been infected on the flight on the way over to New Zealand - there have been eight other cases confirmed from that flight," Dr Bloomfield reveals.

"Genomic sequencing has already linked this case to two other cases from that flight. We are still waiting for genomic testing for two other cases and the other four cases have been effectively been ruled out as a possible source of his infection."

Infected in managed isolation

Another option he became infected in the managed isolation facility in Christchurch.

"A review of CCTV footage from the facility is already underway," Dr Bloomfield announces.

"Modelling shows us that the scenario that presents the lowest risk of anyone getting through managed isolation and having an infection is a 14-day stay, plus testing at day three and day 12, along with very strong infection prevention and control procedures. That is the system we have."

Infected on flight from MIQ facility

Dr Bloomfield says officials are investigating if the man became infected on the flight from Christchurch to Auckland.

This was government-chartered and carrying people from Christchurch Managed Isolation and Quarantine Facilities (MIQFs). There were 86 passengers.

"The passengers from the charter flight from Christchurch to Auckland are being contacted and assessed," Dr Bloomfield says.

"The people from the first nine rows who sat near the case have been asked to self-isolate and have been tested."