The food bug listeria has killed one woman and contributed to the death of another after an outbreak in Hawke's Bay, where it has been found in food supplied to the regional hospital.

Two other people have been infected by the bacterium but have since recovered.

It is not clear where they became infected, but tests last week have shown listeria was present in pre-packaged meat supplied to the hospital.

Hawke's Bay District Health Board is refusing to link the infections with a recall of cold meats produced by Hawke's Bay company Bay Cuisine, where listeria was found earlier this month.

The company is the hospital's sole supplier of pre-packaged meats.

The four victims have all been infected since May. The deaths - of a woman in her 60s and another in her 80s - occurred in the past six weeks.

The hospital withdrew all pre-packaged meats from its kitchen on July 10 after preliminary results came back positive. The results were confirmed on Monday.

The board's director of public health, Caroline McElnay, said the women who died were immuno-compromised, meaning they were more susceptible to the bug than the general population.

The cases were identified on May 9, May 18, June 21 and June 29. Dr McElnay said it was highly unusual to get four cases within such a short period.

There were different types of listeria and just two of those infected - one of whom had died - had the same type. "The organism is very common. We cannot say for sure where the disease was contracted," she said.

Investigations by the DHB and the Primary Industries Ministry had not confirmed a common food source.

The disease took an average of 30 days to show symptoms and was generally only of high risk to those already immuno-compromised, the elderly and pregnant women.

The hospital said no pre-packaged meat was served to patients in the maternity ward.

Health Minister Tony Ryall said he was informed about the "very sad and unfortunate" situation on Monday.

"I have asked the ministry and DHB to ensure that the public health service does everything it can to support the families and learn from this sad experience."

The Primary Industries Ministry's compliance and response deputy director-general, Andrew Coleman, said Bay Cuisine had notified the ministry on Monday that it would issue a voluntary recall of several processed-meat products.

"MPI has implemented a test-and-release programme for ready-to-eat meats at Bay Cuisine and is currently managing any potential food-safety risks to the public."

He advised people either to return recalled meat products to the store where they had bought them, or throw them out.

A link between two listeria deaths and the processed meat had not been confirmed, he said, and "it would be wrong to speculate on a link while inquiries are under way".

The ministry was also investigating a listeria case in Tauranga.

Bay Cuisine has recalled some salami and pepperoni rolls sold by Mad Butcher stores, some hams and some plain-packed leg ham pieces and wholes.

Bay Cuisine director Simon Wills said he was "extremely concerned with the situation".

The company was working with the ministry to identify the source of contamination and was awaiting an independent review of its food preparation procedures.

He said people returning the product would be fully refunded.

The products were sold in Mad Butcher stores nationwide and at Preston's stores in Wellington, Porirua and Palmerston North.

Andrew Preston, of Preston's, said his company had been contacted by Bay Cuisine on Tuesday and had removed all products from its shelves.

Mad Butcher Holdings chief executive Michael Morton said the company voluntarily recalled two products made by Bay Cuisine after it was made aware of higher-than-acceptable levels of bacteria in a corned beef product about 1pm on Monday.

"I've been in the company 15 years and this is the first time we've had [a recall]."

LISTERIA AT A GLANCE

Listeriosis is a serious illness caused by the bacterium Listeria monocytogenes.

It can be very dangerous for pregnant women and their unborn children, newborn babies, frail elderly, and anyone whose immune system is already weakened.

It is often associated with ready-to-eat products such as deli meats and salads, soft cheeses and foods with long refrigerated shelf lives. The bacteria multiply quickly, even in refrigerators.

Symptoms include fever, headache, tiredness, aches and pains. They can also include diarrhoea, nausea and abdominal cramps and, in rare cases, can lead to meningitis and blood poisoning.

It is one of 50 notifiable diseases, which means doctors are legally required to report the illness to local public health authorities.

Last year 21 people died in a listeria outbreak in the United States caused by tainted rockmelons.

- © Fairfax NZ News