One person has died and two people have been hospitalised with listeria in Tauranga, prompting a warning to pregnant women and others at risk.
Authorities are urgently trying to find the source of the dangerous bacteria which can be found in raw fish, processed meat, hummus and many other cold foods.
It is dangerous for newborn or unborn babies, elderly people, or those with poor immunity.
The region's medical officer of health, Neil de Wet, said all three of those who were affected were between 70 and 90 years old.
The person who died already had a terminal condition, he said.
One of the two remaining hospitalised patients has been discharged, and the other remains in hospital in a stable condition.
Three cases were reported to health officials between 12 and 20 July.
It was possible the cases were linked because it was unusual to see three in two weeks, Dr de Wet said. Usually the region had between one and five cases a year.
An investigation with the Ministry for Primary Industries was under way to find the source.
Its compliance director Gary Orr said they will look to see if there is a common food connection.
"Any case of listeria is a worry for us, particularly if there is a link to food ... If it is shown to have a link to food then we will move very quickly to make sure we take that risk food out of the system or alert the public," he said.
"The reality is that listeria is endemic in the environment. It's out there, and if you don't wash fruit before consuming, if you don't wash vegetables or cook them properly you do run the risk of contracting listeria."
The process of elimination for finding the source was painstaking but MPI would be working as quickly as possible to reduce the risk to the public, Orr said.
Public health officers would interview the patients or their families about where they had been and what they had eaten to see if there was a link.
Pregnant women and other groups vulnerable to the disease should follow the usual advice to avoid risky foods, Dr de Wet said.