Listeriosis

Unique identifier / Notation

BI0218

Synonyms

Listeria infection

Listeriosis is a foodborne infection caused by the bacterium Listeria monocytogenes which can be invasive (the more serious form of the disease) or non-invasive (the milder form of the disease). Listeriosis outbreaks occur in all countries and can be a significant public health concern (WHO, 2018).

Primary reference(s)

WHO, 2018. Listeriosis. World Health Organization (WHO). Accessed 14 February 2025.

Annotations

Additional scientific description

Listeriosis is a zoonotic disease, meaning it can be transmitted from animals to humans. This is primarily due to the consumption of contaminated food, as Listeria monocytogenes, the bacterium causing listeriosis, can contaminate various food sources, including meat, dairy, and ready-to-eat foods. There are two main types of listeriosis: a non-invasive form and an invasive form.

Non-invasive listeriosis (febrile listerial gastroenteritis) is a mild form of disease affecting mainly otherwise healthy people. Symptoms include diarrhoea, fever, headache and myalgia (muscle pain). Outbreaks have generally involved the ingestion of foods containing high doses of Listeria monocytogenes (WHO, 2018).
Invasive listeriosis is a more severe form of the disease affecting certain high-risk groups of the population, including pregnant women, immunocompromised individuals (such as those with HIV/AIDS, leukaemia, cancer, kidney transplant and steroid therapy), elderly people and infants. This form of disease is characterised by fever, myalgia, septicaemia, meningitis, and other severe symptoms, including abortion in pregnant women. It is associated with a high mortality rate (20%-30%). The incubation period of listeriosis is usually one to two weeks but can vary from a few days up to 90 days (WHO, 2018).

Listeria monocytogenes is a highly adaptable food-borne pathogen that causes the life-threatening illness listeriosis in infected individuals. Within the host, this bacterium invades cells, escapes into the host cell cytosol and replicates intracellularly (O'Byrne & Utratna, 2010). Unlike many other common foodborne diseases causing bacteria, L. monocytogenes can survive and multiply at the low temperatures usually found in refrigerators. In past outbreaks, foods involved have included ready-to-eat meat products, such as frankfurters, meat spread (paté), smoked salmon and fermented raw meat sausages, as well as dairy products (including soft cheeses, unpasteurised milk and ice cream) and prepared salads (including coleslaw and bean sprouts) as well as fresh vegetables and fruit. Eating contaminated food with high numbers of L. monocytogenes is the main route of infection (WHO, 2018).

Infection can also be transmitted between humans, notably from pregnant women to unborn babies. Pregnant women are about 20 times more likely to contract listeriosis than other healthy adults. It can result in miscarriage or stillbirth. Newborn babies may also have low birth weight, septicaemia and meningitis. People with HIV/AIDS are at least 300 times more likely to get ill than those with a normally functioning immune system (WHO, 2018).

Owing to the long incubation period, it is challenging to identify the food which was the actual source of the infection (WHO, 2018).

In animals, L. monocytogenes is capable of causing septicaemia, neurologic disease, and reproductive disease in a wide range of hosts. Animals are usually asymptomatic carriers of L. monocytogenes. Outbreaks of listeriosis in wildlife species are typically sporadic and associated with exposure to high burdens of the bacterium over a short period of time. Otherwise, clinical signs may arise secondary to immunocompromise, predisposing disease, or excessive environmental stress (WOAH, 2020). The clinical manifestations of listeriosis in animals include rhombencephalitis (or in some cases more disseminated encephalitic changes), septicaemia and abortion, especially in sheep, goats and cattle (WOAH, 2021).

Metrics and numeric limits

Listeriosis is a relatively rare disease with 0.1 to 10 cases per 1 million people per year depending on the countries and regions of the world. Although the number of cases of listeriosis is small, the high rate of death associated with this infection makes it a significant public health concern (WHO, 2018).

The European Centre for Disease Prevention and Control (ECDC) has published a case classification for outbreak management and national epidemiological surveillance (ECDC, 2018).

Key relevant UN convention / multilateral treaty

International Health Regulations (2005), 3rd ed. (WHO, 2016).

Codex Alimentarius (FAO and WHO, no date).

Drivers

Listeriosis is a serious, but preventable and treatable disease. Pregnant women, the elderly or individuals with a weakened immune system, such as people with immuno-compromised status due to HIV, leukaemia, cancer, kidney transplant and steroid therapy, are at greatest risk of severe listeriosis and should avoid high-risk foods. High-risk foods include deli meat and ready-to-eat meat products (such as cooked, cured and/or fermented meats and sausages), soft cheeses and cold smoked fishery products. Listeria monocytogenes is widely distributed in nature. It can be found in soil, water, vegetation and the faeces of some animals and can contaminate foods (WHO, 2018).

Unlike many other common foodborne diseases causing bacteria, L. monocytogenes can survive and multiply at low temperatures usually found in refrigerators. Eating contaminated food with high numbers of L. monocytogenes is the main route of infection. Infection can also be transmitted between humans, notably from pregnant women to unborn babies. L. monocytogenes is ubiquitous in nature and found in soil, water and animal digestive tracts. Vegetables may be contaminated through soil or the use of manure as fertilizer. Ready-to-eat food can also become contaminated during processing and the bacteria can multiply to dangerous levels during distribution and storage (WHO, 2018).

Impacts

Pregnant women, the elderly or individuals with a weakened immune system, such as people with immuno-compromised status due to HIV, leukaemia, cancer, kidney transplant and steroid therapy, are at greatest risk of severe listeriosis and should avoid high-risk foods (WHO, 2018).

Multi-hazard context

L. monocytogenes are ubiquitous in nature and found in soil, water and animal digestive tracts. Vegetables may be contaminated through soil or the use of manure as fertilizer. Ready-to-eat food can also become contaminated during processing and the bacteria can multiply to dangerous levels during distribution and storage (WHO, 2018). Food most often associated with listeriosis include:

foods with a long shelf-life under refrigeration (L. monocytogenes) can grow to significant numbers in food at refrigeration temperatures when given sufficient time); and
foods that are consumed without further treatment, such as cooking, which would otherwise kill L. monocytogenes.

In past outbreaks, foods involved included ready-to-eat meat products, such as frankfurters, meat spread (paté), smoked salmon and fermented raw meat sausages, as well as dairy products (including soft cheeses, unpasteurized milk and ice cream) and prepared salads (including coleslaw and bean sprouts) as well as fresh vegetables and fruits (WHO, 2018).

Risk Management

The control of Listeria monocytogenes is required at all stages in the food chain and an integrated approach is needed to prevent the multiplication of this bacteria in the final food product (WHO, 2018). The challenges for controlling L. monocytogenes are considerable given its ubiquitous nature, high resistance to common preservative methods, such as the use of salt, smoke or acidic conditions in the food, and its ability to survive and grow at refrigeration temperatures (around 5 °C). All sectors of the food chain should Implement Good Hygienic Practices (GHP) and Good Manufacturing Practices (GMP) as well as implement a food safety management system based on the principles of Hazard Analysis Critical Control Points (HACCP).

The World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO) have published an international quantitative risk assessment of Listeria in ready-to-eat foods. This formed the scientific basis for the Codex Alimentarius Commission Guidelines on the Application of General Principles of Food Hygiene to the Control of Listeria monocytogenes in Food (FAO, 2007).

For animals, best practices indicate maintaining proper hygiene at feeding areas, especially where free-ranging ruminants are present, and preventing contamination with faeces; quaternary ammonium compounds, povidone iodine, chlorhexidine, 7.0% ethanol, glutaraldehyde, and sodium hypochlorite are typically effective; efficacy is increased if formulated with ozonated water rather than tap water (WOAH, 2020).

In general, guidance on the prevention of listeriosis is similar to guidance used to help prevent other foodborne illnesses. This includes practising safe food handling and following the WHO Five Keys to Safer Food (WHO, 2006).

Monitoring

The section and the table below offer an overview of monitoring for listeriosis in animals. This information can be used for forecasting within a national early warning system (EWS). Since EWS capacities and processes differ across countries, the most current and specific information regarding EWS should be obtained from the appropriate national or regional agency/authority responsible for disaster management.

Which institution(s) produce(s) Disaster Risk Data/Information?

Ministry of Health, Ministry of Agriculture, Ministry of Livestock, Ministry of Health, FAO Reference Centres, WOAH Reference Centres, WHO

How is the Hazard Observed/Monitored/Forecast?

WHO supports countries to conduct all-hazards strategic risk assessment in the contexts of health emergencies and disasters, which results in the development of a country risk profile. Empowered with the country's risk profile, inclusive of a seasonal risk calendar, countries can anticipate potential emergencies before they occur to trigger early alerts and inform early actions (WHO, 2021).

WHO's Early Warning, Alert and Response System (EWARS) has been designed to improve disease outbreak detection in emergency settings, such as in countries in conflict or following a natural disaster. It is a simple and cost-effective way to rapidly set up a disease surveillance system. EWARS is deployed during an emergency as an adjunct to the national disease surveillance system. WHO works with Ministries of Health and health sector partners to train local health workers to use the system. After the emergency, EWARS should re-integrate back into the national system (WHO, no date)

Through its global early warning system, FAO has been supporting Members with risk monitoring, assessment and forecasting for animal health threats to enhance preparedness and response to animal health threats:

The Global Animal Disease Information System, EMPRES-i+, plays a crucial role in supporting countries with early warning and early detection of animal disease outbreaks. By providing a comprehensive platform for real-time disease tracking, EMPRES-i+, enables monitoring and analysis of animal health threats effectively, collaborating closely with countries and regions on disease information sharing. This supports the dissemination of risk assessments and alerts for evidence-based decision-making.
FAO develops and maintains decision support tools that provide risk maps of existing and predicted risks of animal disease emergence, as well as other threats to the agri-food chain.
Additionally, FAO collaborates closely with international organizations like WHO and WOAH to verify disease information through integrated mechanisms such as the Epidemic Intelligence from Open Sources (EIOS), the Global Early Warning System (GLEWS+), and the World Animal Health Information System (WAHIS) for WOAH-listed diseases. These collaborations allow for the dissemination of early warning alerts and risk assessments to Members, to enable timely responses to potential outbreaks.

FAO empres-i+ https://empres-i.apps.fao.org/diseases

WOAH WAHIS https://wahis.woah.org/#/event-management