Listeria infection

Listeriosis is a rare infection caused by Listeria monocytogenes, an aerobic gram positive rod found in some semi-processed foods including soft cheeses and pate.

Listeriosis is rarely recognised in healthy adults except when pregnant. Pregnant women may also be infected from sheep at lambing time.

It is uncommon. In 1990, there were 24 confirmed cases in 700,000 births in England and Wales.

NICE states that:

• Pregnant women should be offered information on how to reduce the risk of listeriosis by:
  • drinking only pasteurised or UHT milk
  • not eating mould-ripened soft cheese such as Camembert, Brie, and blue-veined cheese (there is no risk with hard cheeses such as Cheddar, or cottage cheese and processed cheese)
  • not eating pâté (of any sort, including vegetable)
  • not eating uncooked or undercooked ready-prepared meals

Summary:

Reservoir:

• gastrointestinal tracts of humans, birds, cattle, sheep and other animals
• widespread in the environment: soil, vegetation, water, silage/sewage, mammal/fish/bird faeces
• occurs in raw foods, food components and ready-to-eat foods: most commonly in foods because of contamination from sites in food production environments

Epidemiology:

• listeriosis is a rare but severe systemic infection that includes bacteraemia, meningitis, and encephalitis and in pregnant women can lead to miscarriage and stillbirth
• most often affects those who have a weakened immune system including pregnant women, their unborn and newborn infants, the elderly and individuals who are immunocompromised by a pre-existing medical condition or treatments for an existing illness
• occasionally, healthy people can become infected
• Listeriosis has a high mortality rate of 20-30% and in the UK is the most common cause of death from a foodborne illness. The annual number of laboratory-confirmed cases of listeriosis averaged 180 a year between 2005-14

Transmission:

• majority of cases are foodborne. Cases and outbreaks have been associated with a variety of foodstuffs, the most common in England and Wales being pre-prepared sandwiches but other foods have included soft cheeses, cooked and processed meats (e.g. pâté and sliced meat), smoked fish, butter, olives and melon in the US
• mother-to-baby transmission is important:
  • in utero transmission,
  • vertical transmission during birth, or
  • person-to-person spread soon after delivery
• direct contact with infected animals can occasionally cause infection
• pregnant women, individuals who are immunocompromised and those (< 1 month and >60 years of age) are more susceptible to infection
• L. monocytogenes can be present in the faeces of approximately 5% of the population but is likely to be transitory

Incubation period

• For invasive disease, the incubation period ranges from 1-70 days

Clinical features:

• Initial symptoms of listeriosis include fever and flu-like symptoms, which may or may not be preceded by a febrile gastroenteritis. Pregnant women may be asymptomatic or have mild symptoms. A person of any age and immune-state may experience any of the following symptoms or remain asymptomatic. Below are the most common presentations for particular patient groups
• Healthy adults and older children:
  • Asymptomatic infection
  • Acute gastroenteritis with fever
  • Non-specific symptoms such as fever, muscle aches, headache
  • (often goes undiagnosed/unrecognised)
• Pregnant women
  • no/mild non-specific flu-like symptoms (as above)
  • foetal loss, stillbirth, pre-term delivery with severe infection in the newborn (some with pre-term delivery) and neonatal meningitis
• Immunosuppressed persons / older adults
  • septicaemia, meningitis or meningo-encephalitis
• Immunocompetent persons can also present with severe disease such as septicaemia or meningitis

Infectivity:

• Not applicable except at and shortly after delivery due to contact (hand or fomites) from an infected infant to an apparently healthy infant who develops meningitis

Guidance for management of meningitis if the causative organism has been identified as Listeria monocytogenes (4)

• for meningitis caused by Listeria monocytogenes:
  • give intravenous amoxicillin or ampicillin for 21 days
  • get advice from an infection specialist on adding intravenous co-trimoxazole for the first 7 days
• after 21 days, stop antibiotics if the person has recovered, or get advice from an infection specialist if they have not

Reference:

1. NICE (2008). Antenatal care.
2. Dept of Health 9.12.1992 PL/CMO(92).
3. PHE (2019). Recommendations for the Public Health Management of Gastrointestinal Infections
4. NICE (March 2024). Meningitis (bacterial) and meningococcal disease: recognition, diagnosis and management