With the Delta variant all household members of a case will usually become infected, unlike previous strains where only some or even no members of the same household would contract the virus.
"That does affect your numbers particularly if you are dealing with large households.
"We did say that we didn't believe we would peak until eight to 10 days [into lockdown]. We're not there yet."
Ardern said extra testing capacity has been set up across the country to cope with the huge demand for testing which has seen long queues at testing sites.
Specific sites were set up for priority vaccination cases.
Ardern suggested people should also check if their local GP was offering testing.
In some areas, 10 times the rate of tests were being done as in the previous week, she said.
Ardern said officials were running down every theory trying to find out how the Delta variant spread from the apparent source in managed isolation.
Two people who passed through an atrium alongside the Crown Plaza isolation facility as the traveller was being checked in are still being sought.
Four have been identified using CCTV and three of them have tested negative.
Those going into MIQ go in through the lobby via the atrium, which is a thoroughfare shared by members of the public, but is divided by a perspex barrier.
Ardern said investigations were under way, but to date transmission had been primarily through droplets so it was understandable that those designing the facilities would think large perspex walls would be sufficient.
"Everything that we've done around our managed isolation facilities has been based on the way that we know Covid-19 has been behaving."
In the mean time, people are not being put in the Crowne Plaza facility.
"Just in case we do find that it has come out through some other means that we have not yet identified - that means that we can address that immediately."
