Listeria Infection: Key Facts About Listeriosis

Medically Reviewed By Michaela Murphy, PA-C
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Listeriosis is a foodborne infection. The bacterium Listeria monocytogenes causes it. Older adults, newborns, pregnant people, and those with a weakened immune system are at the highest risk. People who are otherwise healthy do not generally get a Listeria infection. People who are otherwise healthy do not generally get a Listeria infection.

Treatment involves IV antibiotics, that is, antibiotics administered through a vein.

This article explains listeriosis, including its symptoms, causes, and treatment. 

What is Listeria?

Older woman resting on her side
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Listeria infection is a foodborne bacterial illness. The bacterium lives throughout the environment. You can find it in water, soil, mud, and decaying vegetation. 

Healthy people usually do not generally get seriously ill from a Listeria infection. If healthy people ingest a significant amount of the bacteria through contaminated food, they can develop gastroenteritis and fever.

Listeria can cause serious diseases in susceptible people. The infectious syndromes Listeria can cause include:

  • encephalitis, which is an infection of the brain
  • fetal infections, which can result in loss of the pregnancy, stillbirth, premature birth, and life threatening problems in the newborn
  • gastroenteritis, which is a digestive infection
  • meningitis, which is an infection of the fluid and membranes that surround the brain and spinal cord
  • bacteremia, which is a bloodstream infection and can cause sepsis, a life threatening response to an infection

Doctors refer to Listeria infection that spreads outside the gut as “invasive listeriosis.” In addition to the brain and spinal cord, invasive listeriosis can affect the abdomen, liver, lungs, gallbladder, eyes, heart, bones, and joints.

What are the signs and symptoms of Listeria food poisoning?

Symptoms of Listeria food poisoning vary widely. Healthy people with a Listeria infection may have symptoms of Listeria gastroenteritis. When other symptoms occur, they depend on where the infection is.

Gastroenteritis

When Listeria affects the gut, it can cause the following symptoms:

Invasive listeriosis

When the infection gets outside the digestive tract, symptoms can include:

Newborn listeriosis

Newborn infants with Listeria infection may have the following symptoms:

How do you know you have listeriosis?

Healthy people who are not pregnant do not typically know they have listeriosis. According to the Centers for Disease Control and Prevention (CDC), it is rare for people like this to get very sick from Listeria. Even during pregnancy, symptoms are often mild. Symptoms may only include fever, diarrhea, vomiting, and other flu-like symptoms

If you have symptoms of listeriosis, doctors diagnose the infection with bacterial cultures. This diagnosis involves taking a sample of tissue or fluid and seeing if bacteria grow. Doctors can take samples from amniotic fluid, blood, spinal fluid, and tissues, such as the placenta.

A lab can tell what bacteria are growing and which antibiotics will work best for treatment.

How do you treat listeriosis?

Treating listeriosis requires IV antibiotics. The antibiotic of choice is ampicillin or penicillin G. For people with severe penicillin allergies, Bactrim (trimethoprim, sulfamethoxazole) is an option.

Another option is penicillin desensitization, which involves gradually giving penicillin to avoid an allergic reaction. For meningitis, doctors may add different antibiotics to cover other bacteria that may be causing it.

Other treatments will depend on the symptoms you have.

What causes listeriosis?

The bacterium Listeria monocytogenes causes listeriosis. It is ubiquitous, meaning you can find it anywhere in the environment. This includes soil, water, and contaminated foods.

Unlike most other foodborne pathogens, it can survive and grow under refrigeration. Therefore, most people have had exposure to it at some point. People who are not high risk do not usually get sick from this minimal exposure.

Foods that are most likely to have Listeria contamination include:

  • cold cuts, deli meat, lunch meats, hot dogs, and pate
  • melons
  • raw sprouts
  • refrigerated smoked fish and seafood
  • soft cheeses, such as brie, blue cheese, feta, and queso fresco
  • unpasteurized or raw milk and milk products

How to protect yourself from Listeria food poisoning

Most people are not at high risk for listeriosis. For those that are, avoiding foods that are most likely to carry the bacteria can help protect against it. Cooking these foods can also be helpful, as high temperatures will kill Listeria. Safer versions of these foods include canned and shelf-stable packaging.

Follow these recommendations for preventing Listeria-related foodborne illness:

  • cook meat, poultry, and seafood to recommended temperatures
  • eat cut melon right away and discard it after 4 hours at room temperature or 7 days under refrigeration
  • keep hot foods hot
  • reheat leftovers until steaming
  • throw out opened hot dogs after 1 week
  • throw out opened deli meats or cold cuts after 3–5 days
  • wash fresh fruits and vegetables

What are the complications of Listeria food poisoning? 

Listeriosis is rare, affecting about 1,600 Americans each year. However, it is a very serious infection. With invasive listeriosis, about 20% of people do not survive.

While pregnant people usually do not get a serious infection, it can cause devastating complications, including:

  • loss of pregnancy, which occurs in 20% of cases
  • stillbirth
  • premature labor and birth
  • newborn infection, resulting in death 20% of the time

Frequently asked questions

Who is most at risk for Listeria food poisoning?

Being pregnant is one of the main risk factors for listeriosis. Pregnancy increases the risk of infection by 10 times the risk in the general population. Others at highest risk include older adults and people with weakened immune systems, particularly due to:

How often do people get sick from Listeria?

People who are healthy, not pregnant, and have robust immune systems rarely get very sick from Listeria. Even among high risk people, it is still rare. Listeria causes about 1,600 illnesses each year in the United States.

How long does it take for Listeria to go away?

When listeriosis causes gastroenteritis in healthy, nonpregnant people, diarrhea may last around 5 days. Treatment and recovery from invasive listeriosis both depend on the syndrome and severity.

Early recognition and treatment of listeriosis usually clear the infection. However, it can take time for symptoms of invasive listeriosis to develop after eating contaminated food. It usually takes about 1–4 weeks for invasive listeriosis to develop.

Summary

Listeria monocytogenes is a ubiquitous bacterium that usually does not make people sick. However, certain groups are at high risk of developing listeriosis. This foodborne illness can cause several problems, ranging from gastroenteritis to meningitis.

Immunodeficiency, older age, pregnancy, and being a newborn increase the risk of listeriosis. The illness has a high mortality rate and can cause serious pregnancy complications. Treatment involves IV antibiotics and supportive care.

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Medical Reviewer: Michaela Murphy, PA-C
Last Review Date: 2022 Apr 21
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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