Listeria Monocytogenes: The Facts

Listeria monocytogenes is the pathogen responsible for the foodborne illness listeriosis. The incidence of listeriosis is relatively low. However, Food Standards Agency state this disease causes more deaths in the UK from food poisoning than any other foodborne pathogen and annual costs to the economy are estimated at £245 million.


This deadly pathogen commonly found in the environment has excellent mechanisms for survival. It can grow at L. monocytogenes can grow at temperatures between -1.50C and 420C, although grow at 30C is slow.The organism is also fairly thermotolerant and may be able, under some circumstances, to survive pasteurisation. Food implicated in outbreak include prepacked sandwiches, milk, eggs shellfish, pate, ice-cream, soft cheese, melon and coleslaw. The worst outbreak of Listeriosis was in 1992 where 63 people died after eating contaminated pork tongue in aspic. Most major outbreaks in the UK have involved the consumption of prepacked sandwiches in hospitals.  In response, the Food Standards Agency has produced detailed guidance for reducing the of Listeriosis in hospitals and other care settings.


The European Food Standards Agency (2015) reports cases of listeriosis have increased by 8.6% between 2012 and 2013 and been increasing over the last five years. Public Health England (2015) report a 23% increase in cases reported annually in last decade (2005 -2015) compared to the previous decade (1995-2004).


The disease can be invasive and non-invasive. In most healthy people, listeriosis is non-invasive and leads to a mild fever and gastroenteritis with symptoms passing in three days without the need for treatment (NHS 2015). The Centre for Food Security and Public Health (2005) suggest gastroenteritis in healthy people has an incubation period of approximately 1 to 2 days.


Invasive listeriosis can be more severe and spread to other parts of your body, and is most often recognised in the immunocompromised, the elderly, pregnant women and unborn or newly delivered infants. The Food Standards Agency states most people who develop invasive Listeriosis will end up in hospital and over a third will die. Symptoms arising from invasive listeriosis include sepsis, meningitis, encephalitis, miscarriage and long-term health problems (sequelae).The principle route of infection is through food, and the small intestine is the primary site of invasion.


Food safety and hygiene controls are important to reduce the risk of Listeriosis. Standards of food safety and the microbiological quality of ready to eat foods are higher where HACPP and food hygiene training was in place. Food handlers should have a level 2 award in food safety,


supervisors   a level 3 award and managers a level 4 award. Leadership and management have an important role in setting an appropriate food safety culture. Environmental monitoring and product is also required to verify the food safety management system is working as intended.


Approved suppliers and specifications can be useful reducing contamination of foods purchased by a food business operator. Temperature control is important. Chilled ready to eat food should be kept at 5OC or below throughout the cold chain. Food cooked to a core temperature of 75OC will easily kill this pathogen.  


Cross contamination has been widely associated with outbreaks of listerios. Cleaning and disinfection is critical to prevent the formation of biofilms and potential cross-contamination. Selecting the right disinfectant and following the correct cleaning regime is important to control L. monocytogenes. This organism can be resistant to certain disinfectants and the use of jet washers can spread contamination from drains and floors to food and hand contact surfaces via aerosols that hang in the atmosphere for several hours.


A two–stage cleaning process must be followed to remove chemical and biological residues to prevent initial stages of biofilm formation. Other controls to reduce the risk of L. monocytogenes include regular maintenance, premises and equipment design, and linear workflow. 

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