Listeria Contamination: Serious Threat to Food Manufacturers & Caterers

People at highest risk from listeriosis

Here we look at common listeria contamination causes, high-risk foods and prevention strategies for caterers and food manufacturers. 

In March 2017, two people died and at least four more fell ill following a listeria outbreak in the US. It is believed to have been caused by cheese produced at a creamery in New York state.

This case was linked to a relatively small food producer and local, specialised retailers. However, such cases can affect the largest of manufacturers with, presumably, the most stringent food safety standards.

On September 20th 2016, The Kellogg Company issued a recall for 10,000 cases of Kellogg’s Eggo Nutri-Grain whole wheat waffles, over concerns of possible listeria contamination.

This was one of seven recalls in the USA for possible listeria monocytogenes contamination in the month of September 2016 alone. Is it possible to calculate the damage to a company that will occur when a product is recalled due to a risk of food poisoning?

If a company is robust enough, it is possible for long term recovery through longevity and the fading of consumers’ memories, but in the short term the loss of sales and reputation is devastating. In small organisations it can be a terminal blow for the company.

In the UK and USA, the number of product recalls has almost doubled since 2002 and costs nearly 15.6 billion each year. A recent article in “This is Money” has highlighted the cost of food recalls spiralling in the UK, and adds the tendency of supermarkets to ruthlessly punish the affected suppliers. Most companies over the last 10 years have taken out insurance to cover recall claims, and the largest privately owned firm, Hockton, say that claims have increased exponentially, with some claims running into millions of pounds.

Claims in cases where microbiological contamination have been involved have doubled since 2006, with 309 cases last year. These figures however, do not cover the heartache experienced by small companies caught up in product recall.

A recent Mail Online article stated that a scientific report identified listeria bacteria in NHS sandwiches, citing a money saving trend which reduces the cost of preparing hot food. This is a worrying trend on a number of levels, and listeria is a particularly high risk for hospital patients. Listeria, present in the sandwich filling, was left to multiply when the sandwiches were made and stored for long periods of time in refrigerators before use.

Listeria bacteria

One of the most common sources of food poisoning, listeria is a widely distributed bacteria found naturally in soil and water. Most animals, including approximately 5% of humans, carry the bacteria in their gut, where it causes no harm. When it falls onto the ground or water, in the form of faeces, it can then transfer to foods either by direct contamination, or by the plant taking up the infected water. Listeria has also been found in seawater where it can contaminate fish and shellfish.

The first identifiable outbreak of L. monocytogenes was linked to coleslaw production in Canada in 1981. At least 41 cases were identified with 7 deaths and in 1987-89 a large outbreak of listeriosis in the UK was linked to the consumption of pate with more than 350 cases and 48 deaths.


Why does Listeriosis worry us so much?

Although cases are relatively rare, listeria infections are very dangerous for individuals who are categorised as high risk. These will include older people, those with weakened immune systems, perhaps through illness or cancer treatment, and babies, infants and pregnant women.

Infection with listeriosis is usually divided into invasive and non-invasive categories. Invasive listeriosis, when the bacteria has spread beyond the gastro intestinal tract, can result in septicaemia, encephalitis or meningitis and can cause death. Canadian research has highlighted that the risk of developing invasive listeriosis increases 4 times for those aged 65 – 69 and 9 times for those over 75.

People at highest risk from listeriosis

Young healthy people usually show mild symptoms (non-invasive listeriosis), and this can also be the case for young pregnant women, but the transmission of the bacteria to the developing foetus, either via the placenta or during childbirth, can cause miscarriage, stillbirth, preterm labour and the illness and death of the baby. About 14% of listeria infections occur during pregnancy and death rates of infected infants can be as high as 30%.


What foods are more likely to be contaminated with Listeria?

Listeria, as stated, can be found in soil, water sources and seawater. Farm animals are recognised carriers of listeria. Listeria is psychotropic, that is, it is capable of multiplication and survival in cold temperatures. For that reason it is particularly threatening to RTE foods with extended shelf life in the chiller section.

Slow growth of the bacteria has been recorded at temperatures of 1 °C to 5 °C, or refrigeration temperatures. The maximum growth temperature is 45 °C. The bacteria is not killed by freezing. It will be killed by temperatures above 70°C, but will survive in modified atmospheres and those that lack oxygen.

High listeria risk foods

The increase in case numbers over the years can be linked to the development of the RTE (ready to eat) food ranges. The foods particularly associated with listeria are:

  • RTE deli meats and hotdogs
  • Pates and meat spreads
  • Unpasteurised dairy products
  • Soft cheeses made with unpasteurised milk (eg Feta, Brie, Camembert)
  • Smoked seafood
  • Raw vegetables and unwashed fruits


Precautions to be taken by caterers and food producers

1. Catering

Remember that sewage can be found in “raw” water, therefore rinse all fruit and vegetables in clean treated water before use. This applies to peeled vegetables too.

Scrub skinned products such as melons and cucumbers with a clean brush. Dry the fruit and veg with paper disposable towel.

Wash and disinfect all food preparation surfaces and utensils after handling raw foods.

Remembering that listeria can reproduce at low temperatures, ensure the refrigeration temperature is below 5 °C and frozen foods kept at -18 °C. Test the temperature with a thermometer.

Make sure all fridges are clean. Wipe up any spills and make sure there are no drips of juices or fluids.

Thoroughly cook all meats, and take core temperature readings. Use all RTE foods as quickly as possible and be aware of use by dates on anything in the refrigerator. Cool any leftover food to be re-used quickly and cover prior to placing in the fridge.

Separate all raw meat and fish from cooked and ready to eat foods.

Cooking safely to avoid food poisoning


2. Food Manufacturing

Awareness of the listeria bacteria, its ecology and limitations, should form part of actions taken under HACCP procedures and for compliance with the Food Safety Act 1990. Cleanliness is key to minimising any listeria contamination and disinfection should be undertaken continuously. The effectiveness of these procedures must be verified to ensure safety, through monitoring critical control points (CCPs).

Foods produced should be regularly sampled to ensure they are listeria-free. If it is detected, the line must be closed for deep cleaning. End testing of products should be routine and procedures developed to make sure all involved understand the testing requirements, such as the number of samples, size and frequency of testing samples and the follow up actions.

If correctly manufactured, the product should be free from listeria contamination once produced. Great care must be taken to ensure the “clean” product does not become re-contaminated post-production. Cleaning and disinfection will play a major role here, but so will the personal habits of staff. It is essential that all staff must wash their hands regularly, particularly after visiting the toilet, handling raw meat and vegetables, and touching their nose, face or skin. Contaminated hands have been proved to be the most common vehicle of contaminating foods.

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