Finding a recent case in managed isolation and quarantine (MIQ) or elsewhere on the border that matched this cluster lineage would be strong evidence for the border incursion scenario. We haven’t got any such direct evidence – but this doesn’t mean it didn’t happen.
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Extensive testing and contact tracing determined the earliest case found to date was an Americold coolstore worker who first showed symptoms on July 31, and the initial spread of the cluster centred around this coolstore, which imports frozen goods.
Thus, the third hypothesis is that the virus may have been imported on packaging material, where it could have survived in low temperature conditions, and then gone on to infect a worker at the coolstore.