Officials have shed more light on the mysterious Covid-19 infection at Auckland's St Lukes shopping mall - including a possible link to a bus ride.
It was revealed today that an infected Westfield St Lukes worker may have been on the same bus as another positive case on August 12, which underlined the importance of wearing a mask on public transport.
Earlier, the case - an employee who worked at the mall for a number of days while infectious with Covid-19 - was put "under investigation" after initially being connected to the cluster.
But today, director general of health Dr Ashley Bloomfield said there was new evidence through ESR genomic sequencing to put the two back together.
But there was as yet no known or confirmed epidemiological link to the outbreak, he said, and inquiries continued into the source of exposure.
"One specific line of inquiry is that this case and another case may have been on the same bus, and I'd like to take the opportunity to remind everybody of the value and importance of using masks in places, particularly like public transport."
Authorities were now working with Auckland Transport to locate others who may have been on the same bus - something that was being aided through HOP card data.
Bloomfield couldn't yet confirm where the bus was headed - but pointed out that restrictions came into place soon after.
"This bus journey, the morning of August 12, was just before Auckland went into alert level 3. That's the value of having that wider restriction on movement."
That meant even if there was infection on the bus, other people on the bus should have been at home since the bus journey, he said.
Prime Minister Jacinda Ardern said a discussion has been had about having QR codes on buses, but the HOP card system already provided that data.
Other cities didn't have the same data for bus cards, and Ardern said tracer apps were being looked at in those cities.
A spokesman for Auckland Transport told the Herald that those using public transport in Auckland were "encouraged to register their HOP cards to help with contact tracing, if needed".
"Already, around 83 per cent of people travelling on public transport use a registered AT HOP card, which is amongst one of the highest rates in the world. The card can be used to identify what trips have been taken and where a customer may have 'topped up' its balance," the spokesman said.
"AT is happy to assist health authorities with any information they require.
"To maintain privacy, if we are required to share information under the Health Act, data will be transmitted by secure file transfer protocol."
HOP cards can be registered on the AT website.
The spokesman added that the Ministry of Health had been "strongly encouraging people to wear face coverings when on public transport".
"People are also reminded that under Alert Level 3 physical distancing is required on public transport (2 metres)."
Earlier, Auckland Regional Public Health Services (ARPHS) said there was a "very small possibility" that members of the public may have been exposed to the virus from 10.30 to noon on Wednesday 12 August, before the majority of shops closed for alert level.
"[The employee] visited the Countdown for 10 minutes at around 11.15 am on this morning."
Close contacts of the employee have been identified and are in self isolation.
The employee was also at the mall on the afternoon of August 12, and on August 14, 15 and 17 under level 3 restrictions, but there was no interaction with members of the public, ARPHS said.
People who visited the mall on these days are considered "casual contacts" and do not need to self isolate.
But they should keep an eye out for symptoms of Covid-19, such as a new or worsening cough, sore throat, runny nose, loss of sense or smell, or fever, and call their GP or Healthline if they fall ill.
The St Lukes store was one of two supermarkets hastily closed for deep cleaning this week, after health authorities alerted management that two separate shoppers who had tested positive for the virus had visited the stores.
There are now eight people receiving hospital-level care for Covid-19 - two in Auckland City Hospital, one in North Shore and five in Middlemore.
One person at Middlemore remains in ICU.
One person in Waikato was hospitalised but not related to Covid-19.
There are 143 people linked to the cluster who have been moved into the Auckland quarantine facility. This includes 70 people who have tested positive.
There are now 1315 confirmed cases, and 105 active cases.
The two imported cases have been transferred to the Jet Park Hotel.
There were 15,714 tests conducted yesterday.