Listeria (listeriosis): For health professionals
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Key information
Listeriosis is a bacterial infection caused by Listeria monocytogenes. L. monocytogenes is ubiquitous and exists naturally in the environment. Individuals are usually infected by consuming food contaminated by L. monocytogenes, however it can also be transmitted from an infected pregnant person to their fetus or newborn. Infection with L. monocytogenes has been associated with both sporadic illness and outbreaks in Canada.
Invasive listeriosis is a national notifiable disease. All health professionals are to report cases to their provincial or territorial public health authorities.
Although listeriosis is relatively rare, it causes a disproportionately high number of hospitalizations and deaths among those most at risk of becoming sick with invasive listeriosis compared to other foodborne pathogens. It's important for health care providers to learn about listeriosis and to educate those most at risk of infection including:
- adults ages 60 and over
- immunocompromised people
- people who are pregnant
- caregivers
Clinical manifestations
Signs and symptoms of infection may vary depending on the person and the site of the infection. Most commonly, L. monocytogenes causes a mild illness such as febrile gastroenteritis. Symptoms such as fever, diarrhea and vomiting typically appear 24 hours after eating contaminated food and resolve within a few days. The incubation period can be longer for pregnant individuals, often 4 weeks but potentially up to approximately 70 days after exposure.
Those at increased risk of invasive listeriosis include:
- adults ages 60 and over
- immunocompromised people
- people who are pregnant and their fetuses or newborns
Listeriosis in pregnancy, including neonatal listeriosis
Listeriosis in pregnancy is often characterized by symptoms such as:
- fever
- chills
- fatigue
- malaise
- myalgias
- arthralgia
- diarrhea (watery, non-bloody)
In many instances, the infection in pregnancy can be subclinical. Milder clinical presentations and a longer incubation period make listeriosis more challenging to diagnose in pregnant individuals. Listeriosis in a pregnant individual, regardless of clinical severity, can have severe impacts for a fetus or newborn:
- fetal death
- miscarriage or stillbirth
- premature delivery
- birth of a newborn that dies shortly after birth
Surviving newborns with listeriosis are often classified as "early onset" or "late onset."
Early onset neonatal listeriosis is due to transplacental infection and often presents as pneumonia, sepsis or meningitis. Severe disease can result in widespread granulomas (Granulomatosis infantisepticum).
The source of infection for late onset neonatal listeriosis may be less clear, with the baby potentially infected during birth or after birth (for example, nosocomial or environmental exposure). Late onset neonatal listeriosis often causes meningitis or sepsis.
In both early and late onset neonatal listeriosis, the mortality rate ranges from 10% to 50%.
Listeriosis of the central nervous system
Common clinical presentations of invasive listeriosis include sepsis and meningitis. Other common symptoms of listeriosis of the central nervous system include:
- high fever
- nuchal rigidity
- tremor and/or ataxia
- seizures
The most common form of non-meningitic listeriosis of the central nervous system is encephalitis involving the brainstem (rhombencephalitis).
Transmission
L. monocytogenes is transmitted:
- by ingesting contaminated food
- by touching contaminated food, surfaces or other materials, and then transferring the bacteria to the mouth
- transplacentally from an infected parent to the unborn baby during pregnancy or via the birth canal directly to a newborn during delivery
- from direct contact with infected animals, for example, during the birthing of infected animals or the butchering of infected animals for meat
The predominant mode of L. monocytogenes transmission is ingesting contaminated food. Nosocomial infections and person-to-person transmission (excluding vertical) are recognized but rare. The bacteria has been isolated from ticks and flies. However, arthropod-mediated transmission hasn't been reported.
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Diagnosis
Laboratory testing can confirm infection with L. monocytogenes by isolating the organism from:
- a normally sterile site (for example, blood, cerebrospinal fluid, etc.)
- placental or fetal tissue (including amniotic fluid) in the context of miscarriage or stillbirth
Testing of stool isn't useful for diagnosing invasive listeriosis.
Treatment
Most people with only gastrointestinal symptoms recover from listeriosis without antibiotics. Antibiotics are the primary choice of therapy for treatment of severe human listeriosis. Severe cases may also require additional management and care, based on their clinical presentation and as determined by their health care provider. Individuals with invasive listeriosis typically require hospitalization and treatment.
Prevention
Precautions for individuals most at risk of becoming sick with severe listeriosis include avoiding certain foods that are considered to be higher risk for listeriosis and choosing safer alternatives.
People can help prevent the spread of L. monocytogenes by practicing good hygiene, such as:
- washing their hands with soap and water
- following general food safety tips
- disinfecting environmental surfaces
No vaccine is currently available.
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Surveillance
Health professionals in Canada play a critical role in identifying and reporting cases of listeriosis. Since 2007, invasive listeriosis has been a nationally notifiable disease in all provinces and territories.
Cases are reported to:
- local or regional public health authorities, who then report to the provincial or territorial level as appropriate
- the federal level if they meet the national case definition
Canada uses different surveillance systems to monitor cases of listeriosis. These include:
- the Enhanced National Listeriosis Surveillance Program
- the National Enteric Surveillance Program (NESP)
- the Canadian Notifiable Disease Surveillance System (CNDSS)
- PulseNet Canada
- FoodNet Canada
Invasive listeriosis is an uncommonly diagnosed infection that occurs worldwide. In recent years, about 168 cases of invasive listeriosis were reported annually in Canada.