A salad producer is withdrawing its products and suspending operations at its factories after a batch tested positive for listeria monocytogenes bacteria.

Photo: Supplied

LeaderBrand, which sells a range of salad products including Fresh Plus salads, Value Bag salads and Pam's Fresh Express salads, says the bacteria was found yesterday during regular testing.

Listeria was most likely to affect pregnant women, newborn babies and young children, frail older people, and those with weakened immune systems, the Ministry of Health said.

A full list of products being recalled would soon be available on the Ministry for Primary Industries' website.

LeaderBrand chief executive Richard Burke said while only its Caesar Salad tested positive for listeria monocytogenes, it has taken all its salad products off the shelves at Countdown, New World and Pak'n Save, and from the Subway fast food outlet.

"LeaderBrand Caesar Salad is only one of many product lines, and we are confident none of our other products have been affected," Mr Burke said.

The Ministry for Primary Industries (MPI) has been notified.

Earlier today the company said the recall was just for products issued in the past week, but it has now asked supermarkets to take all of its products off the shelves.

Listeria was soil-borne and could get "into the system" via many different means, he said.

The salad processing plant had been shut down while testing took place to find out exactly how the Caesar range had been contaminated.

"We are reasonably confident that we know where it came from, but until we get further testing and understand the exact cause of this, we can't do anything more except recall all the product."

It would take 24 hours to complete confirmation tests.

Mr Burke would not say if any fast food outlets other than Subway were involved, but said the company had been in touch with all of its customers.

"We can only apologise to our customers and thank them for their support as we work through this," he said.

"We've been in the salad game for 20 years and in business for 40 years and this a major concern for us.

"We're not taking it lightly, we've got a lot of people working on it, ensuring that we get things right and we understand what did occur."

A MPI spokesperson said because listeria could spread through a processing environment, all salads produced by LeaderBrand over a particular time period were being recalled.

"Listeria can be harmful to 'vulnerable' populations if ingested; that includes children under five years of age, adults over 65, pregnant women and people with compromised immune systems."

A Subway spokesperson said all the products have been removed from every store, which might mean they would be out of lettuce stock for a day or two.

"We were notified late last night. We're a bit over-cautious on these kind of things. Our product is unaffected and there is no evidence of any contact at all, but we chose to immediately withdraw all the lettuce as a precaution."

Antoinette Laird from Foodstuffs NZ, the parent company of New World, Pams and Four Square supermarkets, said several bagged LeaderBrand products have been removed from shelves.

"Foodstuffs takes any potential product food safety risk very seriously. The health and safety of our customers is paramount.

"Only once we have total confidence that all product is safe for our customers to consume, will we return it to our shelves."

Countdown spokesperson James Walker said his organisation had taken similar measures.

"Countdown has not received any reports of illness associated with this product. If customers do start to feel unwell, we advise that they seek medical advice from their GP or call the Healthline on 0800 611 116."

Customers who have bought LeaderBrand salad products are being advised to dispose of them, or return them to where they were purchased for a full refund.

Symptoms of infection with listeria bacteria can include mild fever, aches and pains, stomach cramps, vomiting or diarrhoea, according Ministry of Health information.

BRANDS AFFECTED: