Covid 19 Delta outbreak: The key number to look out for in days ahead

Of people infected in the latest coronavirus outbreak, 73 are essential workers.

And if that number grows, it could have major implications for how the country gets through the latest chapter in the pandemic, Covid-19 modeller Shaun Hendy says.

An MIQ worker at Four Points Sheraton Hotel in Auckland has tested positive for Covid-19. Photo / Alex Burton

"The big concern is we get an outbreak in that network of essential workers, obviously across supermarket chains for instance," Hendy said on Sunday.

"They key thing would be to see whether that number is growing."

Hendy, from Te Pūnaha Matatini and the University of Auckland Department of Physics, said it was a never a surprise if a fraction of all positive cases were essential workers.

"The key thing is, have they been interacting with their co-workers and members of the public?"

Currently, essential workers were known to be less than one-fifth of all 429 positive cases in the Auckland cluster.

Hendy said it would be important to observe how locations of interest correlated with likely essential worker shifts.

If a supermarket was deemed a location of interest for many hours, or for an eight-hour block, that likely indicated a worker there had tested positive.

"At the moment, we're not seeing eight-hour periods in supermarkets post-level 4 pop up," Hendy said.

"So hopefully there, essential workers that are caught up in it are already isolating."

Hendy also said it was important for people partaking in their favourite weekend rituals to be conscientious about wearing face masks.

"It's not mandatory outside if you're out on your walk, but there might be places like the local shops that are a bit of a bottleneck."

He advised people to wear face masks when approaching areas that were likely to have more foot traffic than usual.