Otago University public health professor Nick Wilson. Photo / Supplied
Otago University public health professor Nick Wilson. Photo / Supplied
Experts are warning there may have been a number of transmissions of Covid-19 between it entering New Zealand and being first picked up in the community on Tuesday.
It comes as the earliest exposure site, Sumthin Dumplin in Auckland's city centre, suggests Covid may have been lurking in the community for 16 days after a person who has since tested positive for Covid and may have been contagious visited there on August 3.
University of Otago professor of public health Nick Wilson said the Devonport tradesman whose positive test first alerted the Government to it being in the community was "almost certainly not the initial person".
Wilson said there would have been at least one person prior to that either in New South Wales or related to the border in some way who bought it into the community.
"He's almost certainly just one in a chain of transmission whether that's just one or two cases linked back to someone coming from New South Wales or it could be quite a few more. Yes, it's very uncertain."
Wilson said the genomic testing could sometimes show differences in the viruses which would indicate who gave it to whom.
"By looking at it carefully you can see which of the people were infected first because you can't always rely on symptoms."
Microbiologist associate professor Dr Siouxsie Wiles said they were casting the net "very wide" because the country had to find out how many underlying cases there were.
"We need to understand how long this has been in the community. When we think of the first case that was identified, you know, we're in level 4 to stop forward transmission but we need to find out how that person got infected."
She said they may be part of one transmission chain, or there might be several transmission chains and one led to that person.
Otago University epidemiologist Michael Baker told Newstalk ZB a more complex picture was emerging - of who was really the first case and who passed the virus to whom.
Director general of health Dr Ashley Bloomfield told the AM Show he suspected the reason for one of the locations being more than two weeks ago was "precautionary" because one of the cases reporting symptoms might go back for some quite time.
He said while it was possible it may have been in the community for two weeks, based on the current cases there was nothing to suggest that it was in the community earlier than August 11.
Further genome sequencing of these cases and border-related cases expected to be revealed at 1pm would help build a picture of where the sources could be.
