The minister for food safety says three of the four cases of hepatitis A linked to frozen imported berries on sale in New Zealand have come from a single product.
But the product is yet to be publicly named.
Jo Goodhew said she first became aware of the issue in October after the medical officer alerted the Ministry for Primary Industries to a case of hepatitis A.
She said that one case soon became four cases, but it took until November for "questions to be answered and for genotyping to be established that it could be from frozen imported berries."
In Parliament yesterday, Labour food safety spokesman Damien O'Connor asked Ms Goodhew why products had not been recalled, as they had been in Australia nine months ago.
Ms Goodhew said the 31 cases of infection in Australia had been linked to a single product that was different to the product three of the four New Zealand cases had been linked to.
"Here in New Zealand three of the four cases have had the genotyping completed, the fourth is still under way," she said.
"We know for three of the four cases we have genotyping for that they are from the same source, maybe not the fourth, but maybe it is.
"We want to protect all new Zealanders from the possibility of getting it from any frozen imported berries."
She advised New Zealanders to boil the berries, or heat them to more than 85C for at least a minute.
In February, MPI said it was monitoring frozen berry imports after a recall in Australia prompted by cases of hepatitis A.
On Monday, the ministry's director-general issued a statement warning of a "potential risk associated with imported frozen berries" following the four cases "thought to be linked to packaged imported frozen berries".
Frozen berries are often used by cafes in smoothies and other ready-to-eat foods. The ministry says the risks associated with these items are the same as for home-made products and heat treatment will address any potential risk.
Hepatitis A virus is a waterborne and foodborne liver infection for which a vaccine is available.
The disease is spread through contact with faeces of an infected person, such as through failure of an infected food handler to wash hands properly after using the toilet. After consuming the virus, it takes 15 to 50 days for symptoms to appear.
Hepatitis A symptoms include:
• Loss of appetite
• Jaundice (yellow skin)
• Dark urine
• Abdominal pain