Dr Ashley Bloomfield says the possibility of New Zealand's latest outbreak of COVID-19 being caught from the surface of imported goods at a cool store is "unlikely".
The Prime Minister and Director-General of Health announced the four news cases of the virus on Tuesday, New Zealand's first acquired by community transmission in 102 days.
One of these cases was employed at Americold in Mt Wellington, a frozen storage warehouse in which handles imports from overseas.
Recently, some Kiwis have speculated the virus originated from a contaminated surface at Americold, but Dr Bloomfield says other ways of transmission are more probable.
"I still think, and the Prime Minister said this very early on, it's unlikely," Dr Bloomfield said during Thursday's press conference.
"The most likely explanation is person-to-person transmission or more fleeting fomite transmission from an infected surface somewhere and the index case has picked up the virus from there. We are wanting to rule out the cool store link."
He said transmission was more likely at a managed isolation facility, the airport or a port.
Prime Minister Jacinda Ardern also pointed out that COVID-19 would have spread easier between the workers in a cold environment.
On Thursday, 13 new cases of COVID-19 were confirmed including three employees at Americold.
"Cool stores have proven around the world - anywhere that has a cold environment, meatworks have been listed - it's the environment that does make that transmission very effective and very problematic," Ardern noted.
She said the Ministry of Health is currently chasing "all leads" to the "unanswered questions" from the community transmission.
The Ministry of Health has been testing surfaces at the cold storage officers where the latest COVID-19 case worked as a precaution.
Americold's managing director Richard Winnall told Newshub on Wednesday any goods handled in the warehouse would not be touched by consumers as the packaging is multilayered.
All of Americold's employees at the Mount Wellington warehouse were sent home and would be tested for COVID-19. The company's warehouse near Auckland Airport has also been closed.