Listeriosis

What is listeriosis?

Listeriosis is a bacterial infection caused by the bacteria Listeria monocytogenes. Listeriosis is typically a food-borne illness and usually affects those with impaired immunity. Its presentation may range from febrile gastroenteritis to potentially fatal invasive disease, including sepsis, central nervous system infection, and perinatal infection [1].

Listeriosis may also uncommonly present with cutaneous eruptions.

Who gets listeriosis?

Most cases of reported listeriosis are sporadic but a number of outbreaks have occurred [1].

Clinical listeriosis mostly occurs in high-risk groups including [2]:

• Pregnant women and fetuses
• Neonates
• Older people (generally considered as ≥ 65 years)
• Immunocompromised patients due to medical conditions, such as AIDS (or human immunodeficiency virus (HIV) infection), and haematological malignancy
• Patients on immunosuppressive therapies, including long–term corticosteroids and medication following organ transplantation
• Veterinarians and farmers assisting birthing animals, who are also at higher risk of primary cutaneous listeriosis [3].

What causes listeriosis?

L. monocytogenes is an anaerobic gram-positive bacillus found in vegetation, soil, and animals. The consumption of contaminated food is thought to be the main route of transmission. The bacterium can survive acidic, salty, and cold food-processing techniques and can continue multiplying even with proper refrigeration [1]. The incubation period for listeriosis is variable, and outbreaks have occurred 3–70 days following exposure to contaminated food products [4]. The median incubation period is approximately 3 weeks.

The following foods are considered high-risk products [4]:

• Unpasteurised dairy products
• Soft cheese
• Pâté
• Raw or smoked seafood
• Pre-packed cold salads
• Delicatessen foods that have not been reheated adequately
• Sprouted seeds and raw mushrooms.

L. monocytogenes may also be transmitted from mother to baby, via the placenta or vaginal infection [1].

Rarely, L. monocytogenes may also be transmitted from animals to humans [1].

Most cases of cutaneous listeriosis in adults result from direct inoculation of the skin [3]. This is most commonly seen in veterinarians or farmers who come in contact with birthing animals, products related to animal conceptions and births, or soil carrying the bacteria. Cutaneous listeriosis may also result from invasive diseases spread through the bloodstream of individuals with impaired immunity [3].

Foods that may carry listeria 

What are the clinical features of listeriosis?

In immunocompetent individuals, non-invasive listeriosis typically manifests as febrile gastroenteritis with self-limiting nausea, vomiting, and diarrhoea [2].

• In older patients and those with impaired immunity, invasive listeriosis most frequently presents as sepsis or central nervous system infection with fever and neurological signs.
• Listerial bacteraemia or septic emboli from listerial endocarditis can lead to localised infections including hepatitis, cholecystitis (inflammation of the gallbladder wall), peritonitis (inflammation of the abdomen organ linings), splenic abscess, pericarditis, pleuritis (inflammation of the lung outer lining), endophthalmitis (inflammation of the eye sockets), and osteomyelitis.
• Cellulitis, lymphadenitis, and conjunctivitis from direct inoculation with listeriosis have all been described [2].

Maternal T-cell immunity is most affected during the third trimester and this is when listeriosis in pregnancy typically occurs [1].

• Mothers tend to develop flu-like symptoms but may be asymptomatic [5].
• Perinatal infection can result in miscarriage, stillbirth, preterm delivery, neonatal sepsis, or meningitis.
• Neonatal listeriosis may be classified as early-onset, which occurs within the first week of life and is most often associated with sepsis, or late-onset, which is commonly associated with meningitis [5].
• Granulomatosis infantisepticum is a severe form of generalised neonatal infection, which can cause granulomatous lesions involving multiple organs, including the skin [5].

Clinical features of cutaneous listeriosis

Cutaneous listeriosis typically presents as purpuric, papulopustular, or vesiculopustular eruptions that are painless and non-pruritic [3].

• Cellulitis with abscess formation has less commonly been described [6].
• Eruptions generally occur on exposed areas, such as the hands and forearms [3].
• The median time from exposure to the onset of rash is 2 days.
• Many patients experience systemic symptoms, of which fever is the most common.
• Associated regional adenopathy (enlargement of an organ) and lymphangitis have been reported [7].
• In neonates, the rash is typically more widespread. Granulomatosis infantisepticum presents with an erythematous rash with widespread small, pale papules [8].

How is listeriosis diagnosed?

Listeriosis is diagnosed by isolating L. monocytogenes from a site that is normally sterile, such as the patient's blood, cerebrospinal fluid (the fluid between the brain and spinal cord), gastric washings (results of a stomach pump), amniotic fluid (the liquid that surrounds the fetus in the womb), meconium (the first fecal material from a fetus), placenta or fetal tissue specimens [1]. The bacterium may also be isolated from a skin biopsy.

• Listeria may be present asymptomatically as normal vaginal and gut flora; therefore, samples of these are not useful in diagnosis [9].
• Microscopy and culture or polymerase chain reaction (PCR) may be used for detection.
• Molecular subtyping may help determine the association between isolates from cases and any products that test positive for L. monocytogenes [4].
• Serology testing for listeriosis is not very specific or sensitive [1].

Histopathology may demonstrate:

• Mild spongiosis and lymphocytic exocytosis or pustules with subcorneal intraepidermal collections of neutrophils [10].
• Mixed acute and chronic inflammatory infiltrate in the dermis including prominent macrophages with intracellular and free coccobacillus (a short and oval bacillus) on Gram stain or haematoxylin and eosin (H&E) stain.
• Granulomas in granulomatosis infantisepticum [8].

An elevated white-cell count on full blood examination is usually found.

Imaging may show abscesses on the patient's internal organs, such as the liver and brain.

What is the differential diagnosis for cutaneous listeriosis?

Listeriosis presents like many other infectious diseases that cause fever and constitutional symptoms. The differential diagnosis for cutaneous listeriosis is wide and may include:

• Folliculitis
• Contact dermatitis
• Localised herpetic infection.

Differentials to consider based on histopathology include infections with intracellular microorganisms, such as granuloma inguinale, rhinoscleroma, and leishmaniasis [10].

What is the treatment for listeriosis?

Listeriosis is treated with antibiotics.

Penicillin alone, or with gentamicin, is considered the drug of choice for the treatment of listeriosis. Vancomycin, meropenem, and linezolid have also been used successfully in case reports [1,11,12,13]. In patients who are allergic to penicillin, trimethoprim-sulphamethoxazole, or erythromycin may be used [1]. L. monocytogenes is resistant to cephalosporins.

The duration of treatment varies depending on the patient's age and the location and severity of the illness.

There is limited evidence on the role of antibiotics in primary cutaneous listeriosis, but it has been proposed that a 5–7 day course of oral amoxicillin or trimethoprim–sulfamethoxazole may be warranted [3].

Listeriosis should be notified to the relevant local authorities [4]. If contaminated products are implicated, these may need to be recalled.

How can listeriosis be prevented?

Immunisation for listeriosis is not currently available.

• The risk of exposure to listeriosis may be minimised through hygienic food preparation and storage.
• It is recommended that pregnant women and immunocompromised individuals avoid high-risk food products.
• Wearing protective equipment, such as gloves, when working with livestock or gardening may assist in preventing cutaneous listeriosis.

What is the outcome for listeriosis?

Listeriosis is usually a self-limiting disease in immunocompetent individuals; however, the mortality rates in invasive disease may be as high as 20% [14]. One third of cases of listeriosis in pregnancy result in miscarriage or stillbirth [1].

Primary cutaneous listeriosis usually resolves without long-term consequence [3].