Listeriosis
What is Listeriosis?
Listeriosis is a serious bacterial infection caused by eating food contaminated with Listeria monocytogenes. This bacteria can survive and even grow in cold temperatures, making refrigerated foods a common source. While healthy adults rarely get severely ill, listeriosis can be dangerous for pregnant women, newborns, older adults, and people with weakened immune systems.
The infection occurs when the bacteria enters your body through contaminated food and begins to multiply. Listeria has a unique ability to invade and survive inside immune cells called monocytes and macrophages. This allows the bacteria to spread through your bloodstream and potentially reach your brain or other organs. Your immune system responds by producing more monocytes, which shows up as elevated levels in blood tests.
Most cases are linked to deli meats, soft cheeses, smoked seafood, and raw produce. The bacteria can contaminate food during processing or packaging. Even properly refrigerated food can harbor Listeria because cold temperatures do not kill it. Understanding your risk and monitoring your immune response through blood testing helps catch infections early.
Symptoms
- Fever and chills that appear suddenly
- Muscle aches and fatigue
- Headache and stiff neck
- Confusion or loss of balance
- Nausea, vomiting, and diarrhea
- Convulsions in severe cases
- Flu-like symptoms in pregnant women
- Miscarriage or stillbirth in pregnant women
Some people experience mild symptoms that resolve on their own within a few days. Pregnant women may only have mild flu-like symptoms but can still pass the infection to their baby. Symptoms typically appear 1 to 4 weeks after eating contaminated food, though they can start as early as the same day or as late as 70 days after exposure.
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Causes and risk factors
Listeriosis happens when you eat food contaminated with Listeria monocytogenes bacteria. Common sources include unpasteurized dairy products, soft cheeses like feta or brie, deli meats and hot dogs, smoked seafood, and raw or unwashed produce. The bacteria can survive in soil, water, and animal intestines, then spread to food during farming, processing, or preparation. Cross-contamination in kitchens and food facilities also spreads the bacteria.
Your risk increases if you are pregnant, age 65 or older, or have a weakened immune system from conditions like HIV, cancer, diabetes, or kidney disease. Taking medications that suppress your immune system, such as steroids or chemotherapy drugs, also raises your risk. Pregnant women are about 10 times more likely to get listeriosis than the general population. Newborns can contract the infection from their mothers during pregnancy or delivery.
How it's diagnosed
Doctors diagnose listeriosis by testing samples from your blood, spinal fluid, or other body tissues for the presence of Listeria bacteria. Blood cultures remain the most common diagnostic tool. Your doctor may also order a complete blood count to check for elevated monocytes, a type of white blood cell that increases when your body fights this specific infection.
Rite Aid offers blood testing that measures your monocyte levels as part of our flagship panel. Elevated monocytes can indicate an active listeria infection or other immune responses. If you have symptoms of listeriosis or recently ate recalled food, testing helps identify the infection early. Early detection allows for prompt treatment and reduces the risk of serious complications.
Treatment options
- Antibiotics such as ampicillin or penicillin for confirmed infections
- Intravenous antibiotics for severe cases or high-risk patients
- Hospitalization for pregnant women, newborns, or immunocompromised individuals
- Supportive care including fluids and rest for mild cases
- Avoiding high-risk foods during and after treatment
- Proper food handling and cooking to prevent reinfection
- Regular monitoring of monocyte levels during recovery
Concerned about Listeriosis? Get tested at Rite Aid.
- Simple blood draw at your nearest lab
- Results in days, not weeks
- Share results with your doctor
Frequently asked questions
Deli meats, hot dogs, soft cheeses made from unpasteurized milk, smoked seafood, and raw sprouts pose the highest risk. Refrigerated pâtés, meat spreads, and pre-cut melons can also harbor Listeria. The bacteria can grow even in properly refrigerated foods, so eating high-risk foods without heating them increases your chances of infection.
Symptoms usually appear 1 to 4 weeks after eating contaminated food. Some people develop symptoms within 24 hours, while others may not get sick for up to 70 days. This long incubation period makes it difficult to identify the exact food source without careful tracking of what you ate.
Yes, but healthy adults rarely develop serious illness from listeriosis. Most experience mild symptoms like diarrhea and fever that resolve within a few days. The infection becomes dangerous primarily for pregnant women, adults over 65, and people with weakened immune systems.
Listeria bacteria invade and multiply inside monocytes, a type of white blood cell. Your body responds by producing more monocytes to fight the infection. Elevated monocyte counts in your blood test can indicate an active listeria infection, though doctors confirm the diagnosis with bacterial cultures.
No, you cannot catch listeriosis from another person through casual contact. The infection spreads only through eating contaminated food. However, pregnant women can pass the bacteria to their unborn baby during pregnancy or to their newborn during delivery.
Doctors treat listeriosis with antibiotics, usually ampicillin or penicillin. Healthy adults with mild symptoms may not need antibiotics and recover on their own. Pregnant women, newborns, and immunocompromised patients typically receive intravenous antibiotics in the hospital to prevent serious complications.
Yes, proper food safety practices reduce your risk significantly. Heat deli meats and hot dogs to steaming hot before eating, avoid unpasteurized dairy products, wash produce thoroughly, and keep your refrigerator at 40°F or below. Clean cutting boards and utensils after contact with raw meat to prevent cross-contamination.
Listeriosis during pregnancy can cause miscarriage, stillbirth, premature delivery, or life-threatening infection in the newborn. Pregnant women may only experience mild flu-like symptoms themselves. If you are pregnant and suspect exposure to contaminated food, contact your doctor immediately for testing and possible preventive antibiotics.
Most people do not need routine testing for listeriosis. Get tested if you develop symptoms after eating high-risk foods or foods involved in a recall. Pregnant women and immunocompromised individuals should discuss testing with their doctor if they have any concerning symptoms or known exposure.
Yes, cooking food to an internal temperature of 165°F kills Listeria bacteria. Reheating deli meats, hot dogs, and leftovers until steaming hot makes them safe to eat. However, foods eaten cold or raw, like soft cheeses and pre-cut produce, remain risky unless they are made from pasteurized ingredients and handled properly.