Food safety authorities are still yet to identify which brand of frozen berries caused three New Zealanders to contract Hepatitis A.
The public has been advised to boil frozen berries before eating them, after the disease was confirmed in three people who lived in different parts of the country.
New Zealand Food Safety's deputy director-general Vincent Arbuckle told Checkpoint the link between Hepatitis A infection and frozen berries had been well-documented in other countries.
He said the three people who had contracted the virus all consumed smoothies with frozen berries regularly.
"There's been careful checking with the three cases, their food history, they're in different parts of the country so we know they've never met each other, they haven't travelled which is often a history for hepatitis a," he said.
"So there's a pretty good likelihood that frozen berries are the key factor in these cases."
However, while he said a lot of effort had gone into identifying the brand of frozen berries, it had been challenging due to the length of time it took to show symptoms of Hepatitis A - which could be up to 50 days after consuming a contaminated berry.
"These are consumers who are quite heavy users of smoothies and frozen berries and their purchasing history over the period of time has been multiple brands," he said.
"It's important we do accurately identify the product because then consumers can relax and not worry about other products. At this stage we just don't have enough certainty on a particular brand and a particular batch."
He said some countries from which berries were imported, such as Peru and Chile, were higher risk as there were much higher rates of Hepatitis A than in New Zealand.
Cases could potentially be more widespread, but authorities were not certain yet, Arbuckle said.
Boiling frozen berries was the only way to eliminate the risk of Hepatitis A and Arbuckle said this was particularly important for the elderly, pregnant people and those with chronic liver conditions.
"The virus is extremely persistent, so freezing does not affect or kill the virus off," he said.
"The only thing that kills the virus off is heat treatment, so the virus will happily live away in your berries frozen in your fridge for as long as you keep them there."