Eyeing up that packet of salami, cold ham or beef cuts at the supermarket for a tasty sandwich?

You might want to think again. A just-published study has found 15 per cent of prepacked ready-to-eat red meat in New Zealand was contaminated with listeria, a food-borne bacteria that can cause illness.

Scientists from the Institute of Environmental Science and Research carried out a microbiological survey of packed red meats - such as shaved ham and beef cold cuts - on sale.

A total of 1485 samples were collected, and each was tested at the end of its stated shelf life against New Zealand's Food Standards Code.

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Researchers looked for the pathogens salmonella, staphylococci and several species of listeria. None breached standards for salmonella or staphylococci, but 15.5 per cent of the pre-cooked meat samples tested contained listeria monocytogenes, which causes the illness listeriosis.

Healthy adults and children usually do not have any symptoms from consuming listeria, but the Ministry of Health website says pregnant women, babies, the elderly and those with weakened immune systems are in danger of falling severely ill.

Symptoms include vomiting, diarrhoea and flu-like reactions.

Pregnant women in particular are warned not to eat anything that could be contaminated with the pathogen - including hummus, pre-made salads and cold meats - because of the risk of miscarriage, stillbirth or premature labour.

Listeria scares are a common reason for food products to be recalled. Just last month a raw milk drink was recalled over listeria fears, and in March the entire range of LeaderBrand salads was recalled from supermarkets after listeria was found in its Caesar salad.

In 2015 a popular shaved ham brand was recalled after tests found it contained the pathogen.

The researchers said their findings highlighted that there might be problems in the way some ready-to-eat meat was being packed or processed.

Better hygiene practices and more effective "risk mitigation strategies" might also be needed, they said.

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The contaminated samples came from eight of the 33 producers tested. The Herald has asked the Ministry for Primary Industries for comment on whether it will be investigating those producers and whether they are complying with safety standards.

The study was published in the Journal of Food Protection on October 4.

However an MPI spokeswoman said there was no cause for alarm and the ministry was confident of the country's food safety standards.

Though just published in the journal, the research was from a 2011 study and officials had followed up with food producers where businesses had not met food safety requirements, she said.

"MPI and ESR were not able to publish the report at the time of its writing because it coincided with a prosecution undertaken against a company that provided meat containing listeria monocytogenes to a hospital.

"MPI continues to monitor food safety in this area and all producers of ready-to-eat meats need to meet our strict food safety laws."

This included businesses registering with MPI, running a robust food safety programme which outlined how they would manage the risk of Listeria and being regularly verified checked by MPI-approved verifiers to ensure they were meeting requirements.

"MPI also monitors food borne illnesses on an annual basis and there has been no increase in food borne cases of listeria since 2011. In fact, in 2016 there were no food borne illness outbreaks linked with listeria."