Listeria Infection: Signs and Symptoms

Listeriosis is a potentially life-threatening infection caused by some species of listeria bacteria. But the signs and symptoms of a listeria infection vary widely depending on a person’s age and health status. All of this can make diagnosis a little tricky.

“Listeriosis primarily affects pregnant women and their newborns, older adults, and people with weakened immune systems,” says Jennifer Hunter, DrPH, an epidemiologist who has worked with the Centers for Disease Control and Prevention’s Epidemic Intelligence Service. “Other people can be infected with listeria, but they rarely become seriously ill.”

What are the signs of a listeria infection, and how do you know if you have listeriosis? Here’s what everyone should know about listeriosis symptoms.

When adults and kids with healthy immune systems get listeriosis, they may not experience any symptoms at all. “Healthy people usually do not become ill from a listeria infection, and if they do have symptoms, they are often mild,” says Rob Danoff, DO, a family physician at Tillman Family Practice in Bensalem, Pennsylvania.

For these patients, their healthy immune system takes care of the invading listeria bacteria without much fuss. But if symptoms do emerge, they tend to resemble a mild flu or gastrointestinal (GI) bug.

Those symptoms may include:

Fever
Watery diarrhea
Nausea
Headache
Aches in joints or muscles (1)

Children tend to experience fever and vomiting, and adults are more likely to experience diarrhea and joint pain. (1)

In some people, symptoms may take up to two months to emerge, Dr. Danoff says. But typically, symptoms show up 24 hours after someone has eaten a food contaminated with Listeria monocytogenes (the specific strain of Listeria that makes people sick). Those symptoms tend to last between one and three days before subsiding on their own. (1)

These symptoms are what doctors refer to as “nonspecific” — meaning they’re associated with many different ailments and so are not an obvious sign of listeriosis. Also, because these symptoms resolve on their own, most cases of listeriosis in healthy adults are likely never formally diagnosed.

People with weakened immune systems are at much greater risk from a listeria infection. It actually takes a smaller number of the infection-causing bacteria to cause an infection. Anyone undergoing chemotherapy or dialysis, as well as those taking steroids or immunosuppressant drugs, are in this group of people who are considered “immunocompromised.” This group also includes patients with kidney or liver disease, HIV or AIDS, or any other condition that interferes with normal immune functioning. ( 2)

In these patients, very early symptoms of a listeriosis infection could include some or all of the GI or flu-like symptoms mentioned above. While these symptoms don’t warrant treatment in healthy people, immunocompromised patients should tell their doctor immediately to prevent a more serious infection. (3)

Apart from those early and mild flu-like symptoms — which not all patients will experience — listeriosis can show up among immunocompromised people in a number of ways. Two of the most common are sepsis (usually from blood infection) and meningitis (inflammation of the lining that covers the brain and spinal cord). Both of these complications are life-threatening. (4)

While less common, an invasive listeriosis infection could also cause endocarditis (inflammation of the heart), localized infections (including ones on the skin or in the eyes), and other complications. (4)

“People 65 years and older are four times more likely than other people in the United States to get a listeria infection,” Hunter says.

Why? “As people age, their immune systems and organs aren’t as able to recognize and rid the body of harmful germs,” she explains. Older adults are also more likely than younger people to suffer from diseases like cancer or diabetes, or to be taking drugs that reduce their immune function.

Also, stomach acid is an issue. “Stomach acid, which plays an important role in killing germs and reducing the risk of illness, decreases as people get older,” Hunter explains.

While any of the above GI or flu-like symptoms could show up in an older person with a listeria infection, some other signs of listeriosis include headaches, a stiff neck, confusion, loss of balance, and convulsions. (3) While these symptoms could also indicate some other health issue, if there is a risk that an older adult has been exposed to listeria, these shouldn’t be ignored because infections that get more invasive can be very serious and sometimes fatal.

Listeriosis usually causes a mild, flu-like illness for pregnant women, Hunter says. This illness could include all the symptoms mentioned above. But many pregnant women have no symptoms at all. (3)

While a pregnant woman’s immune system will often handle listeria bacteria with ease, “a listeria infection is very dangerous for the unborn baby,” Danoff says. Miscarriage, stillbirth, premature birth, and serious illness at time of birth are all potential risks. So if someone who is pregnant is experiencing symptoms, seeing a doctor as soon as possible is important.

You or your doctor may suspect you’ve been infected with listeria based on the signs and symptoms you’re experiencing — and if you’ve been exposed to something potentially contaminated with listeria bacteria. But it can still be difficult to differentiate from other types of bacterial infections. (5)

Your doctor can test your blood, cerebrospinal fluid, or placenta (if you are pregnant) to confirm a listeria infection. (6)

You read about a local listeria outbreak in your area, and you think you might have eaten the contaminated food item. Or you’re feeling rotten, and you’re worried the suspect hunk of cheese or maybe-too-old piece of meat you ate last night could have been harboring some harmful listeria microorganisms.

In either case — and even if you’re not experiencing any symptoms — tell your doctor. That’s true whether you’re a healthy adult or you’re a member of one of the at-risk groups mentioned above.

“Quick diagnosis and treatment is often very effective in helping those affected feel better and get back to their good health,” Danoff says — before the infection potentially gets worse. Also, your doctor can notify public health authorities who monitor listeria concerns and outbreaks. That could help protect other people who may have greater risks than you do.

When you call your doctor, it will be helpful to have a list of the potentially contaminated foods you may have eaten, as well as a log of any symptoms you’ve noticed.

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