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Listeriosis: Causes, Symptoms & Treatment

Listeriosis is a bacterial infection caused by Listeria monocytogenes, transmitted through contaminated food, and particularly dangerous for pregnant women and immunocompromised individuals.

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Things worth knowing about "Listeriosis"

Listeriosis is a bacterial infection caused by Listeria monocytogenes, transmitted through contaminated food, and particularly dangerous for pregnant women and immunocompromised individuals.

What is Listeriosis?

Listeriosis is an infectious disease caused by the bacterium Listeria monocytogenes. These bacteria are widespread in the environment – found in soil, water, and animal feces – and can contaminate a wide variety of foods. In healthy adults, the illness is often mild or even asymptomatic, but it can be life-threatening for certain high-risk groups.

Causes and Transmission

Infection most commonly occurs through the consumption of contaminated food products. Foods most frequently associated with listeriosis include:

Raw milk products and soft cheeses
Raw or smoked meat and fish (e.g., smoked salmon)
Ready-to-eat foods such as deli meats and salads
Insufficiently heated vegetables or sprouts

Unlike many other bacteria, Listeria monocytogenes can multiply even at refrigerator temperatures (0–4 °C / 32–39 °F), making food safety particularly challenging. Person-to-person transmission is generally not possible; however, an infected pregnant woman can pass the bacteria to her unborn child.

Risk Groups

While healthy adults often experience only mild symptoms or none at all, the following groups are considered high-risk individuals:

Pregnant women and their unborn children
Older adults (over 65 years of age)
Immunocompromised individuals (e.g., those with HIV, cancer, or organ transplants)
Newborns

Symptoms

Symptoms of listeriosis vary depending on the severity of the infection and the individual affected:

Mild Forms (Non-Invasive Listeriosis)

Fever, nausea, and vomiting
Diarrhea and abdominal cramps
Flu-like symptoms

Severe Forms (Invasive Listeriosis)

Meningitis (inflammation of the membranes surrounding the brain): severe headache, stiff neck, sensitivity to light
Encephalitis (brain inflammation): confusion, altered consciousness
Septicemia (bloodstream infection): high fever, chills, circulatory failure
In pregnant women: premature birth, miscarriage, or stillbirth

The incubation period – the time between infection and the onset of symptoms – is typically 1 to 4 weeks for severe forms, though it can be shorter or longer.

Diagnosis

Diagnosis is typically established by detecting Listeria monocytogenes in body fluids. The following diagnostic methods are used:

Blood culture: Detection of bacteria in the blood when septicemia is suspected
Lumbar puncture: Examination of cerebrospinal fluid when meningitis is suspected
Stool culture: In cases of gastrointestinal symptoms
PCR testing: Rapid molecular detection of the pathogen

Treatment

Listeriosis is treated with antibiotics. The first-line agents include:

Ampicillin (often combined with gentamicin in severe cases)
Amoxicillin as an alternative
In cases of penicillin allergy: Trimethoprim-sulfamethoxazole (TMP-SMX)

The duration of treatment depends on the severity of the illness and may last several weeks in invasive forms. Cephalosporins are not effective against Listeria and should be avoided. Severe cases require inpatient hospital treatment.

Prevention and Food Safety

Since listeriosis is primarily foodborne, hygiene measures are essential for prevention:

Heat food thoroughly (above 70 °C / 158 °F at the core)
Avoid raw milk products and soft cheeses (especially for high-risk groups)
Handle raw meat, fish, and seafood carefully
Maintain the cold chain and avoid storing food for too long
Wash hands regularly and clean kitchen surfaces thoroughly
Prevent cross-contamination between raw and cooked foods

In many countries, listeriosis is a notifiable disease, meaning confirmed cases must be reported to public health authorities.

References

World Health Organization (WHO): Listeriosis – Fact Sheet. Available at: www.who.int (2022)
European Centre for Disease Prevention and Control (ECDC): Listeriosis – Annual Epidemiological Report 2022.
Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 9th Edition. Elsevier, 2019.

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