Two elderly Hawke's Bay women have died after contracting listeria, a food-transmitted illness found in meat supplied to the Hawke's Bay Hospital.
Two other people were diagnosed with listeria, but have recovered from the notifiable disease.
Four patients with listeria presented at the Hastings hospital between May and June. Napier company Bay Cuisine Limited issued a recall notice in relation to a variety of meat products that may contain the rare and deadly bacteria.
The company supplied ready-to-eat meat products to the hospital kitchen and cafeteria, but the Hawke's Bay District Health Board said it was still unclear if the patients had contracted the illness while in its care. But they also could not completely rule it out.
Health board CEO Kevin Snee said: "It is fair to say this is a very unusual situation. The last thing we want for is a very rare and unusual event to be creating alarm. There is no need for it."
The health board said listeria was only dangerous to pregnant women, their babies, the elderly and people with a lowered immune system. It is a common bacterium found in dust, soil, water, plants, sewage and animal droppings.
The health board said ready-to-eat meat products were never served in the maternity ward.
Four patients with symptoms of listeria went to hospital on May 9 and 18, and June 21 and 29. The two women, one aged in her 60s and one her 80s were both "immune-compromised" and died in June and July respectively, within a week to 10 days of first arriving, said Hawke's Bay District Health Board Director of Population Health Dr Caroline McElnay.
Infectious Diseases physician Dr Andrew Burns said one woman "definitely" died from listeria, and for the other it was a "significant" factor in her death.
Dr McElnay said test results received on Monday showed there were three different "strands" of the disease in the four patients. The women who died had different strands.
"For us to get four cases over a period of two months is really, really unusual. When you have a suspected cluster of listeria outbreak the most likely cause would be a food source."
There were only 25 cases of the disease in New Zealand each year.
The Ministry of Primary Industry investigated the "internal processes" of the hospital's food supply. Test results were positive.
"We have identified listeria with products sold to us. We are still investigating those further and working with the MPI as to what those mean," Dr McElnay said.
She said Bay Cuisine was the company they purchased ready-to-eat products from, but now they were "cooking meat and slicing it ourselves".
Ministry general compliance and response deputy director Andrew Coleman said the Ministry oversaw Bay Cuisine's voluntary recall of salami, pepperoni and ham products.
"MPI wants to ensure any unsafe food is not available for sale and that people do not eat any of the recalled products they may have bought already."
Investigations are still underway to determine how Bay Cuisine's products - that also supply to meat giant Mad Butcher and a range of other retailers including schools, clubs, restaurants and rest homes - were linked to the outbreak.
Dr Snee said the board needed to wait for investigation results before a health notice was issued.
"We want to make sure the public is aware, particularly those at risk," he said. "The first results we got back on typing [of listeria strands] was on Monday."
Asked why it had taken until today to let the public know, Dr Snee said: "We got the results on Monday and were considering them over the next 24 hours and now we are here. I think that is not a long time."
Dr Burns said a complicating factor was that listeria symptoms took up to 70 days to appear, and therefore the cause was harder to find than other types of food poisoning.
He said the deceased's family members were being briefed as information became available.
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