Prime Minister Jacinda Ardern has reviewed her comments when she said was frustrated a Covid-infected person continued working at KFC and will not be apologising.

Case L, the sister of a Papatoetoe High School student, wasn't isolating at home and went to work at KFC Botany three days before she tested positive for the virus.

She said she was never told to isolate and only her sister received a text message saying she needed to be tested and isolate.

Ardern said about 15 texts and phone calls were made to the family.

"In my mind everyone at Papatoetoe High School getting a test felt really clear to me," Ardern said.

Ardern said if Case L's sister, Case I, had been tested when directed to by the school and the public health unit the situation could've been avoided.

"I'll go back to look at what we could have done in addition to that message."

The Section 70 order came into effect amid the second round of testing at the school.

Case L told Discovery the Prime Minister's comments - that she should have been self-isolating - were "upsetting", and she wanted an apology.

"It's not fair on our end that we're getting all this backlash for something that we haven't actually done," she told Discovery.

Ardern's office said letters from public health were sent to the family on February 17 and 19 saying they needed to be tested. Case L's family said such advice was never received.

"If they tried to contact us multiple times and send us letters and stuff, where is this evidence?" she told Discovery.

Meanwhile, whether or not Auckland is dealing with a bigger Covid-19 cluster will not be known until the next day or two, when a group of gymgoers are tested for the virus for the first time tomorrow.

People who were at City Fitness Papatoetoe at the same time as a young man, who later tested positive for Covid, are considered to be casual plus contacts.

The last time the 21-year-old was at the gym, inside Hunters Plaza, was on Friday (February 26) between 3.25pm and 4.30pm.

As casual plus contacts, they need to have a test on or after day five from the date that they were last exposed to the case, the Ministry of Health says.

The official definition of a casual plus contact is someone who has been exposed to a case where there may be a higher risk of transmission - but who does not meet the criteria of a close contact.