Symptoms of Listeria

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Not everyone who gets infected with Listeria will have symptoms. However, you are more likely to be hospitalized with the symptoms of Listeria than with the symptoms of other stomach bugs like norovirus or salmonella. Anyone who has had food poisoning knows the symptoms of a listeria infection (listeriosis) all too well.

The bacteria can cause some pretty unpleasant gastrointestinal distress like diarrhea, abdominal cramps, and fever. Pregnant women are at particularly high risk due to susceptibility listeria infection and consequences of a severe case.

Listeria symptoms
Illustration by Brianna Gilmartin, Verywell

Frequent Symptoms

Listeriosis can affect different people in different ways. Most healthy adults (including pregnant women) and children infected with the bacteria won’t show any signs at all. When they do, the symptoms they experience often resemble a mild case of the flu or gastrointestinal discomfort and include:

  • Fever
  • Diarrhea
  • Headache
  • Nausea and/or vomiting
  • Fatigue
  • Muscle aches
  • Abdominal cramps

These symptoms typically appear within a few days after eating contaminated food, though it’s not unheard of for symptoms to show up 30 days or more after becoming infected. These flu-like symptoms often last about one to three days.

When the infection spreads beyond the gut—a condition called invasive listeriosis—it can lead to more serious symptoms that often require hospitalization. These can take a little longer to appear (one to four weeks).

  • Stiff neck
  • Confusion
  • Loss of balance
  • Septicemia (a serious infection in the blood)
  • Meningitis (swelling in the lining of the brain and spinal cord)
  • Encephalitis (brain swelling)
  • Other localized infections (such as in the bone, skin, or eye)
  • Convulsions

These symptoms are serious and are more common in vulnerable populations like older adults, newborns, and those with weakened immune systems. Listeriosis (invasive and non-invasive) in healthy individuals is rare.

Rare Symptoms

It’s uncommon, but listeriosis can sometimes lead to grave consequences, including multi-organ failure and death.

According to a study published by the Centers for Disease Control and Prevention, about 21 percent of reported cases are fatal. This type of serious consequence occurs nearly exclusively in high-risk individuals or fetuses.

Complications

Some groups are more likely to have serious cases of listeriosis. These primarily include those with weaker immune systems, such as pregnant women, newborn babies, the elderly, and people living with immune-compromising medical conditions.

Pregnant Women

Pregnant women (especially Hispanic women) are significantly more likely to get listeriosis than other adults. However, if they have any symptoms at all, most pregnant women have only mild symptoms including diarrhea or nausea, backache, fever, headache, and malaise.

The biggest threat due to a listeria infection in pregnant women is the severe consequences it can have for their babies.

Listeriosis during pregnancy can lead to miscarriage, stillbirths, and premature birth.

About 20 percent of women diagnosed with listeriosis during pregnancy will experience fetal loss. However, because many listeria infections are mild or asymptomatic, this rate might be skewed towards the more severe cases that are more likely to be diagnosed.

Because of the high risk that listeriosis poses to the fetus, doctors typically recommend pregnant women avoid (or heat up to kill bacteria) foods known to be sources of listeria outbreaks like sprouts or lunch meat.

Newborn Infants

If a mom is infected with listeria during the very late stages of pregnancy, she could spread the bacteria to her new baby in utero or while giving birth.

Even if the mom didn’t have a serious case of listeriosis, an infection could be particularly dangerous for a newborn infant.

Symptoms in newborns can be hard to detect but can range from mild fussiness and poor feeding to life-threatening illness. About 3 percent of newborns infected with listeria die because of it. Listeriosis symptoms in older, otherwise healthy kids are rare.

Older Adults

Adults over 65 years old make up the majority of listeriosis cases in the United States.

As adults grow older, it gets harder and harder for their bodies to fight off germs. The immune system isn’t as robust as it used to be, and many adults acquire chronic health conditions that can affect the body’s defenses.

Thus, older adults are left vulnerable to a wide range of infections, including foodborne illnesses like listeria. Not only are they more likely to get physically sick and present symptoms (adults over 65 are four times more likely to get listeria than the general population), but they are also more likely to have severe consequences as a result of the illness.

People with Weakened Immune Systems

Age isn’t the only thing that can affect the immune system. Certain medical conditions or medications can also make it easier to get sick with listeria.

Roughly three-quarters of people under 65 years old who aren’t pregnant who contract listeriosis have some kind of underlying medical condition that affects their immune system, such as kidney disease or chemotherapy treatments.

These individuals are more likely to get seriously ill or die from a listeria infection. 

When to Call Your Doctor

A wide range of natural and processed foods have been identified as sources of previous listeriosis outbreaks. Ready-to-eat cold meats, “raw” milk, and soft cheeses are common sources. If you think you’ve recently eaten food potentially contaminated with listeria, you should call your doctor. Also call your doctor if:

  • you start presenting symptoms within two months of eating the suspected food, particularly illness with a stiff neck.
  • have a compromised immune system due to age, medical condition, or medications.
  • are pregnant or have a newborn baby.

It’s likely not necessary for you to see a doctor or get tested for listeria if you don’t show symptoms and/or you are not in an at-risk group. That said, talk to your doctor if you have questions about your risk for serious listeriosis or if you are not sure if you should be seen. Antibiotics can be effective against the infection, particularly for pregnant women to protect their babies.

A Word From Verywell

While listeria outbreaks are often widely publicized when they occur, listeriosis is actually very rare in the United States. Most non-pregnant, otherwise healthy individuals usually do not get sick from the bacteria, even when they have eaten food they know to be contaminated with it. If you are presenting symptoms and are uncertain, however, always be sure to check with your doctor.

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