There was a four-day cross over in managed isolation between a returnee with the more infectious South African strain of Covid-19 and the Northland woman they passed the virus to.
Genome testing indicates it was a direct transmission, but exactly how the virus spread between the two currently remains a mystery.
The carrier returned a positive day three test but Doctor Ashley Bloomfield says that person was free to move around the Pullman Hotel before they got the result.
Director General of Health Dr Ashley Bloomfield discusses the case with Lisa Owen.
