Listeria monocytogenes in ready-to-eat products: advice for health professionals
Source: gov.uk (2025-04-24)

How healthcare professions should manage patients with invasive listeriosis

This guidance is for healthcare professionals who are managing patients with invasive listeriosis. It can also be used in the management of patients at higher risk of invasive infection who have eaten ready-to-eat products that are potentially contaminated with Listeria monocytogenes.

Background

Listeria monocytogenes (LM) is a rare cause of food poisoning. Individuals have to ingest a relatively high dose of LM to cause illness.

The incubation period, that is the period between ingesting LM and developing symptoms, ranges from 24 hours to 70 days. Therefore, while the vast majority of cases are likely to present with symptoms in the first 2 weeks after eating contaminated food, a few may have a delayed presentation.

Most infections are acquired through foodborne transmission, typically by eating contaminated foods such as soft cheeses, pâté, smoked fish, chilled sliced meats and other chilled ready-to-eat products (pre-packed sandwiches, salads, pre-cut fruit, frozen desserts). LM is regularly found in food production units.

All NHS trusts, independent sector healthcare providers, care homes, and other health and care facilities are food business operators that have an obligation to serve safe food to their patients or clients. Low levels of LM in food products (within the regulatory limit) will not cause illness in most individuals; however, it may cause serious infections in people who are severely immunocompromised.

People who are at higher risk from severe listeria infection

Most healthy individuals who ingest LM will be asymptomatic or experience mild illness such as flu-like symptoms or gastroenteritis. These symptoms usually pass within a few days without the need for treatment.

However, certain people are at greater risk of developing invasive disease (invasive listeriosis) after ingesting LM. These include:
- pregnant women
- newborn babies
- older people (risk increases with age, most notably when aged over 80)
- cancer
- organ transplants
- people taking oral steroids
- people undergoing immunosuppressive or cytotoxic treatment including biologics and chemotherapy
- people with uncontrolled HIV infection
- people with uncontrolled diabetes
- people with chronic liver or kidney disease
- people with alcohol dependency
- people with iron overload
Clinical presentation of invasive listeria infection

The signs and symptoms of invasive listeriosis depend on the site of the infection and the person affected. Clinical presentations can include sepsis, meningoencephalitis, septic arthritis, osteomyelitis and prosthetic graft infections. These can be preceded by febrile gastroenteritis. Listeriosis can also cause miscarriages and still births in pregnant women who may be asymptomatic or have only mild symptoms. Newborn babies may acquire perinatal infection including neonatal sepsis and meningitis. Mortality of invasive disease can be up to 40%.

Management of patients from high-risk groups with gastroenteritis without invasive listeriosis after consuming a potentially contaminated product

The aim of treating these individuals is to minimise the risk of invasive disease by reducing the amount of LM present in their gastrointestinal system.

Adults from high-risk groups with gastroenteritis, but who do not have invasive disease, for whom no other cause of illness is known, should be tested with blood cultures and can be treated with oral amoxicillin 1g taken 3 times per day for 14 days. If the individual has a penicillin allergy, options include oral co-trimoxazole 960mg twice per day for 14 days in non-pregnant adults. In pregnant women with potential LM exposure and penicillin allergy contact your local microbiologist for advice.

Management of patients with suspected or confirmed invasive listeria infection

Cases with confirmed invasive disease should be treated with intravenous antimicrobials according to local standard protocols. The most appropriate antimicrobial agent can be discussed with your local microbiologist.

Clinicians should liaise with their microbiologists for advice on management of patients admitted with suspected invasive disease or those with risk factors for severe disease.

Advice is also available from the duty medical microbiologists at Colindale, UK Health Security Agency at xxx@xxx.xx (mailto:xxx@xxx.xx)

Food safety advice for individuals in at-risk groups

The best way for patients in at-risk groups to protect themselves is to follow the guidance about which foods they should avoid or be aware of, which foods should be handled with care, and to follow advice on appropriate handling, storage and preparation of foods. It is recommended that those in specific high-risk groups should avoid eating certain chilled, ready-to-eat products. More information is available on the NHS (https://www.nhs.uk/conditions/listeriosis/) website and the Food Standards Agency (https://www.food.gov.uk/listeria) website.

References
- Brouwer MC, van de Beek D. ‘MONALISA: a grim picture of listeriosis’ The Lancet Infectious Diseases doi: 10.1016/S1473-3099(17)30054-3
- Elinav H, Hershko-Klement A, Solt I and others. ‘Pregnancy-associated listeriosis: many beliefs, few facts’ The Lancet Infectious Diseases: volume 15, issue 10, pages 1,128-30 doi: 10.1016/S1473-3099(15)00302-3
- Ooi ST, Lorber B. Gastroenteritis Due to Listeria monocytogenes (https://doi.org/10.1086/429324) Clinical Infectious Diseases 2005: volume 40, issue 9, pages 1,327-1,332
- Committee Opinion No. 614: ‘Management of pregnant women with presumptive exposure to Listeria monocytogenes’ Obstetrics and Gynecology 2014: volume 124, issue 6, pages 1,241-1,244 doi: 10.1097/01.AOG.0000457501.73326.6c. PMID: 25411758
- Craig AM, Dotters-Katz S, Kuller JA, Thompson JL. ‘Listeriosis in Pregnancy: A Review’ Obstetrical and Gynecological Survey 2019: volume 74, issue 6, pages 362-368 doi: 10.1097/OGX.0000000000000683. PMID: 31216045.
- Scobie A, Kanagarajah S, Harris RJ, Byrne L, Amar C, Grant K, Godbole G. ‘Mortality risk factors for listeriosis – A 10 year review of non-pregnancy associated cases in England 2006-2015’ Journal of Infection 2019: volume 78, issue 3, pages 208-214 doi: 10.1016/j.jinf.2018.11.007. Epub 2018 Dec 5. PMID: 30528872.