Listeriosis is infection by Listeria monocytogenes — a foodborne bacterium that is particularly dangerous because it can grow at refrigerator temperatures, allowing contaminated ready-to-eat foods to become heavily colonised despite proper refrigeration. Most healthy adults exposed to Listeria either have no symptoms or experience mild gastroenteritis. However, in vulnerable populations (pregnant women, the elderly, and the immunocompromised), listeriosis causes invasive disease — bacteraemia, meningitis and fetoplacental infection — with a 20-30% case fatality rate.

Why is pregnancy such a high risk?

Pregnancy profoundly suppresses T-lymphocyte-mediated immunity (essential for controlling intracellular pathogens like Listeria) — this allows Listeria to multiply and spread through the body even in otherwise healthy women. After maternal bacteraemia, Listeria crosses the placenta to infect the fetoplacental unit — causing miscarriage, intrauterine fetal death, preterm labour or neonatal listeriosis. The mother often has only mild flu-like symptoms while the fetus may be fatally affected. This is why listeriosis is catastrophic in pregnancy.

What foods should pregnant women avoid?

WHO and EFSA recommend that pregnant women avoid: unpasteurised soft/surface-ripened cheeses (brie, camembert, blue cheese, goat cheese); deli meats, pâté and cold cuts (unless thoroughly cooked until steaming); cold-smoked fish (cold-smoked salmon, trout); pre-packaged salads and coleslaw; hummus; soft serve ice cream; raw/undercooked meat and seafood. Safe alternatives: hard cheeses (cheddar, parmesan); pasteurised cheese products; thoroughly cooked meats.

How is listeriosis treated?

Invasive listeriosis: IV ampicillin (or amoxicillin) — the drug of choice. Addition of gentamicin (for synergy — combined bactericidal effect) is recommended for severe cases, particularly meningitis and fetoplacental infection. Duration: bacteraemia 2 weeks; meningitis 3-4 weeks; brain abscess 6 weeks. Alternative if penicillin-allergic: TMP-SMX (trimethoprim-sulfamethoxazole). CRITICAL: cephalosporins are NOT effective — Listeria has intrinsic resistance. Empirical meningitis therapy in at-risk patients must include ampicillin.

How is listeriosis detected in food?

Food testing involves environmental swabs from food production facilities and product testing — L. monocytogenes must be undetectable in 25g of ready-to-eat food. Whole-genome sequencing (WGS) of Listeria isolates from patients and food samples allows highly accurate traceback of outbreak sources. The EU/EEA Listeria surveillance network and ECDC regularly detect and investigate multi-country listeriosis clusters through WGS analysis.

How does GMJ News cover listeriosis?

GMJ News covers WHO listeriosis data, the refrigerator-temperature growth property, pregnancy risk and safe food guidelines, cephalosporin resistance (critical clinical point), ampicillin treatment, major outbreak examples, and WGS outbreak investigation. Listeriosis is a food safety priority — particularly for Georgian soft cheese and cured meat producers — directly relevant to PHIG's food safety accreditation programme.

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Listeriosis

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

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Listeriosis — caused by Listeria monocytogenes, an environmental bacterium uniquely capable of growing at refrigerator temperatures — causes approximately 23,000 cases and 5,500 deaths per year globally with a case fatality rate of 20-30% in vulnerable groups, making it proportionally the most lethal foodborne pathogen (WHO). Pregnant women face approximately 100-fold higher risk of invasive listeriosis than the general population, with vertical transmission causing miscarriage, stillbirth, preterm birth and devastating neonatal listeriosis. Sources: unpasteurised soft cheeses, deli meats, smoked fish, pre-packaged ready-to-eat foods — all capable of harbouring L. monocytogenes even when refrigerated.

Key messages

20-30% case fatality — most lethal foodborne pathogen

Listeriosis has a case fatality rate of 20-30% in vulnerable groups — the highest of any common foodborne pathogen. Pregnant women face approximately 100-fold higher risk of invasive listeriosis than the general population (WHO).

Grows at refrigerator temperatures

Listeria monocytogenes is uniquely dangerous because it multiplies at refrigerator temperatures (1-10°C) — meaning properly refrigerated ready-to-eat foods can become heavily contaminated over time, unlike most other foodborne pathogens.

Ready-to-eat foods — the risk category

High-risk foods: unpasteurised soft cheeses (brie, camembert, blue cheese); deli meats and cold cuts; smoked fish (cold-smoked salmon); hummus and other ready-to-eat products. Pregnant women and immunocompromised individuals should avoid these.

Pregnancy — catastrophic consequences

Maternal listeriosis typically causes only mild flu-like illness in the mother but can cross the placenta to infect the fetus — causing miscarriage, stillbirth, preterm birth or neonatal listeriosis (meningitis, septicaemia — high mortality).

Ampicillin is first-line

Listeria is intrinsically resistant to cephalosporins (a critical point — do not use ceftriaxone for empirical meningitis if Listeria is suspected). Ampicillin (± gentamicin for synergy) is the treatment of choice.

Large outbreaks from contaminated food

Major listeriosis outbreaks have occurred from contaminated deli meats (US 1998-99: 101 cases, 21 deaths), melons (US 2011: 147 cases, 33 deaths), soft cheese and cold-smoked fish. Traceback and food recalls are the primary outbreak responses.

Key statistics

~23K

listeriosis cases/year globally

WHO

5.5K

listeriosis deaths/year globally

WHO

20-30%

case fatality rate in vulnerable groups

WHO

100x

higher risk of invasive listeriosis in pregnant women vs general population

WHO

0-45°C

Listeria growth temperature range — survives at refrigerator temperature (4°C)

WHO/Food safety

Intrinsic

cephalosporin resistance — critical for empirical treatment

WHO/Clinical

Listeriosis risk by patient group — relative risk vs general population (WHO)

Source: WHO. Pregnant women bear the highest relative risk; neonates and the elderly the highest absolute mortality.

Glossary of key terms

Listeria monocytogenes
WHOA Gram-positive, non-spore-forming, facultatively intracellular bacillus — ubiquitous in soil, water and vegetation. Unique features: grows at refrigerator temperature (1-10°C); survives wide pH range and high salt concentrations; multiplies to dangerous concentrations in refrigerated ready-to-eat foods over time. Thirteen serovars — serovars 1/2a, 1/2b, 4b cause >95% of human listeriosis.

Listeriolysin O (LLO)
ResearchA pore-forming cytolysin secreted by L. monocytogenes — critical for intracellular survival. LLO disrupts the phagosomal membrane, allowing L. monocytogenes to escape into the cytoplasm, where it hijacks actin polymerisation to propel itself and spread cell-to-cell.

Fetoplacental listeriosis
WHO/MaternalL. monocytogenes crosses the placenta — infecting the fetoplacental unit after maternal bacteraemia. Can cause: miscarriage (any trimester); intrauterine fetal death; premature labour; neonatal listeriosis (early-onset: bacteraemia, respiratory distress — from birth; late-onset: meningitis — 2-3 weeks after birth, possibly from postnatal exposure).

Cephalosporin resistance
WHO/IDCritical clinical point: L. monocytogenes is intrinsically resistant to all cephalosporins (including ceftriaxone). This is clinically dangerous in empirical meningitis treatment — standard empirical bacterial meningitis therapy (ceftriaxone ± vancomycin) will miss Listeria. All empirical meningitis regimens in at-risk patients (age >50, immunocompromised, pregnancy) MUST include ampicillin or amoxicillin.

Food safety regulations
EFSA/FDAListeria is a zero-tolerance pathogen for ready-to-eat foods in the EU and most HICs — L. monocytogenes must be undetectable in 25g of product throughout shelf-life. Manufacturers must implement hazard analysis critical control point (HACCP) systems to control Listeria contamination. Environmental monitoring of food production facilities for Listeria is essential.

Outbreak traceback
WHO/ECDCListeriosis outbreaks are investigated using whole-genome sequencing (WGS) to link cases to a common source. WGS has dramatically improved outbreak detection — identifying clusters of cases with identical or nearly identical genomes even when cases are geographically dispersed over months.

Latest GMJ coverage

Listeria Outbreak in Pregnant Women Linked to Ready-to-Eat Sandwiches Reveals Food Safety Gaps

11/06/2026

Listeriosis

Key messages

Key statistics

Glossary of key terms

Latest GMJ coverage

Frequently asked questions 12 Q&A — structured for Google featured snippets and AI discovery

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