Listeriosis

Listeriosis is a bacterial infection primarily caused by Listeria monocytogenes, though L. ivanovii and L. grayi have been reported in specific cases. This infection can lead to severe illnesses like sepsis, meningitis, or encephalitis, sometimes causing lifelong harm or death. Populations at higher risk include the elderly, foetuses, newborns, and immunocompromised individuals. Pregnant women are particularly vulnerable, with risks of stillbirth, spontaneous abortion, or preterm birth. Although listeriosis can cause mild, self-limiting gastroenteritis and fever, severe cases necessitate medical attention.

Signs and Symptoms

Listeriosis primarily affects older adults, immunocompromised individuals, pregnant women, and newborns. Symptoms typically include fever and muscle aches, often preceded by diarrhoea or other gastrointestinal symptoms. The bacteria often spread from the intestines to the bloodstream or other body sites, leading to invasive infection. Symptoms can vary based on the affected population:

• High-risk individuals (excluding pregnant women): Symptoms can include fever, muscle aches, headache, stiff neck, confusion, loss of balance, and convulsions.
• Pregnant women: Typically experience mild, flu-like symptoms. However, infections can lead to miscarriage, stillbirth, or life-threatening newborn infections.
• Previously healthy individuals: Exposure to a large dose of Listeria can result in noninvasive illness, manifesting as diarrhoea and fever.

Cause

Listeria monocytogenes is ubiquitous in the environment and is primarily acquired through the ingestion of contaminated food products such as raw meat, dairy products, vegetables, fruit, and seafood. Soft cheeses and unpasteurised milk are common sources. The bacteria enter the host via the gastrointestinal tract, penetrate intestinal cells, and spread systemically. The pathogen can escape from phagosomes into the cytoplasm, using the host cell's actin for intracellular movement and cell-to-cell spread. This mechanism often leads to systemic infection, especially in immunocompromised individuals.

Diagnosis

Diagnosis typically involves culturing the bacteria from blood or cerebrospinal fluid (CSF). In cases of central nervous system (CNS) infection, Listeria can be isolated from these fluids.

Prevention

Preventing listeriosis involves safe food handling, thorough cooking, and reheating ready-to-eat foods until steaming hot. High-risk groups, such as pregnant women and immunocompromised individuals, should avoid unpasteurized pâtés and soft cheeses (e.g., feta, Brie, Camembert). Pasteurised dairy products like cream cheese, yoghurt, and cottage cheese are considered safe. Spraying foods with LISTEX P100 bacteriophage, which targets L. monocytogenes, is another preventive measure used in the food industry.

Treatment

Treatment of listeriosis includes prolonged antibiotic administration, primarily ampicillin and gentamicin. Bacteraemia is treated for two weeks, meningitis for three weeks, and brain abscess for at least six weeks. The overall mortality rate is 20–30%, with a significant risk of foetal loss or neonatal death in pregnancy-related cases.

Epidemiology

The incidence of listeriosis in the United States was 2.5–3 cases per million population annually in 2004–2005, with pregnant women accounting for 30% of cases. The incidence has been declining in the U.S. but increasing in Europe due to changing eating habits. There are four main clinical syndromes: infection during pregnancy, neonatal infection, CNS infection, and gastroenteritis. Cardiac involvement is rare but possible.

Recent Outbreaks

Notable outbreaks include the 2002 U.S. outbreak linked to turkey deli meat, the 2008 Canadian outbreak associated with Maple Leaf Foods, and the 2011 U.S. outbreak from contaminated cantaloupes. More recent outbreaks include the 2015 Blue Bell ice cream contamination, which led to three deaths, and the 2017–18 South African outbreak, resulting in 180 deaths. In 2018, an outbreak linked to frozen vegetables affected several European countries, and in 2019, a processed-meat outbreak in Spain resulted in multiple hospitalisations and deaths.

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Self-assessment MCQs (single best answer)

Which bacterium is primarily responsible for causing listeriosis?

Which population is particularly vulnerable to listeriosis during pregnancy?

What are common sources of Listeria monocytogenes contamination?

What is a typical diagnostic method for listeriosis?

Which food product is NOT recommended for high-risk individuals to avoid listeriosis?

Which antibiotics are primarily used to treat listeriosis?

Which symptom is common among high-risk individuals with listeriosis?

What is the estimated mortality rate of listeriosis?

Which preventive measure involves using a bacteriophage to target Listeria monocytogenes in foods?

Which country experienced a significant listeriosis outbreak linked to frozen vegetables in 2018?