Calls to Healthline's dedicated Covid-19 information line have more than quadrupled in recent days, leading to increased wait times for callers.

A 56-year-old woman from Northland tested positive for Covid-19 after completing the required 14 days of managed isolation at the Pullman Hotel in Auckland.

The woman twice tested negative while at the facility before being released on January 13. Before developing symptoms, she travelled to a number of places around the southern part of Northland.

A full list of those locations, including two new shops - Carpet Court and Farmers in Whangarei - is at the bottom of this story.

Andrew Slater, chief executive of National Telehealth Service, which runs Healthline, said the average call wait time after the 4pm press conference was up to 38 minutes.

In December 2020, the average wait time for the Covid Information Line in December 2020 was 1 minute and 6 seconds.

Just over 200 of the 1867 calls to Healthline came through the Covid-19 line on January 23, while the following day almost 1000 of the 2,674 phone calls received came through the Covid-19 line.

Slater said a large number of the calls received were from people asking about the locations visited by the Northland Covid-19 case.

The list covers a period from January 14 - the day after she left MIQ - to January 22 and includes nearly 30 supermarkets, clothing and electronic stores, cafes, restaurants, a gallery, plant centre, museum, pharmacy, vehicle testing station and tavern.

"Many callers were asymptomatic, but wanted to know if they should be tested because they had visited the locations both within the time windows of concern and outside of these," Slater said.

The service called in additional staff both yesterday and today to cope with the increase in call volumes.

As of 2pm Monday, Healthline had answered more than 2,000 calls in total.

Meanwhile, Dr Bloomfield told Newstalk ZB's Heather du Plessis-Allan that while it's now known that the Northland woman caught the virus at the managed isolation facility, it will be investigated just how she caught it.

"What we do know is the whole-genome sequencing of the infection she's got directly matches that of someone else who was in the managed isolation facility at the same time and on the same floor, just a few rooms down," he said.

He said one focus of the investigation would be on shared spaces in managed isolation facility.

He said there was no evidence, such as CCTV footage, showing where the two people came into contact, but health officials "are not leaving any rock unturned".

While he's wasn't sure if it is the case at the Pullman, he said some managed isolation facilities put occupants in vans to transport them to the location where they can complete their physical activity.

"That would be of course one of the places we would be looking."

He said the investigation would review what mix of people are put into those vans.

"Whether they are people, some of whom, might have arrived just recently, tested negative, but have recently, mixed with people who've been there a while, and I guess that is one of the opportunities there could be for cross-infection so we'd want to just shut that down."

When pushed by du Plessis-Allan on how many people have caught Covid-19 in managed isolation facilities, Bloomfield said he doesn't have the exact number but it was a "small" amount.0

Asked whether there should be a "crackdown" on shared spaces in MIQ facilities, Bloomfield said it wouldn't be a crackdown, but a carefully review of how they're used, and whether there is mixing of people who have just arrived with people who've been there some time.

"What we've seen here the person who was leaving on the 13th has been infected by someone who arrived just a few days earlier and tested positive on day 3. They were on the same floor. So, of course, we'll want to look at what is it that could be a risk here for transmission inside the facility and the use of shared spaces is one areas we could look at."