"However, Listeria infection during pregnancy can lead to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn. People who are not pregnant may experience headache, stiff neck, confusion, loss of balance, and convulsions, in addition to fever and muscle aches." (CDC, October 2024)
What is Listeria and Why is it Dangerous?
Listeria is a bacterial foodborne pathogen that can be contracted through commonly consumed foods. The infection is caused by the bacteria Listeria monocytogenes, which unlike other foodborne pathogens, can survive and multiply at refrigerator temperatures (4°C), making it particularly concerning. It can be life-threatening for people with weakened immune systems, especially pregnant women, the elderly, and immunocompromised patients.
Listeria bacteria live in soil and water, and infection occurs through consuming contaminated food. Unlike other foodborne pathogens, Listeria has an unusually long incubation period of 1-6 weeks, making it difficult to trace the source of infection. According to the Centers for Disease Control and Prevention (CDC), Listeria infection ranks as the third leading cause of death from foodborne illness in the United States, highlighting its severity.
What Are the Symptoms of Listeria?
Symptoms of Listeria infection can vary widely depending on the infected person's condition. One particularly dangerous aspect is that healthy individuals may not display any noticeable symptoms.
Common Listeria Symptoms
Common symptoms of Listeria infection include:
- Fever and chills: The most common symptom seen in most infected people.
- Muscle aches: Flu-like muscle pain throughout the body.
- Nausea and vomiting: Digestive symptoms that may occur after food consumption.
- Diarrhea and abdominal pain: Gastrointestinal symptoms presenting as diarrhea and stomach pain.
- Headache: Persistent severe headaches may occur.
These symptoms typically last for about 1-7 days before resolving naturally in many cases. However, in certain high-risk groups, they can progress to more serious complications.
Invasive Listeriosis Symptoms
If the bacteria spread through the bloodstream to other organs, developing into more serious invasive listeriosis, the following additional symptoms may appear:
- Stiff neck: Particularly when it progresses to meningitis, neck stiffness is a common symptom.
- Confusion and mental cloudiness: Cognitive function may be affected, resulting in a confused state.
- Loss of balance: Difficulty maintaining balance may occur.
- Convulsions: In severe cases, seizures may occur.
- Meningitis: Inflammation of the membranes surrounding the brain and spinal cord, causing severe symptoms.
- Sepsis: Blood infection that can be life-threatening.
These invasive listeriosis symptoms are more common in people with weakened immune systems and require immediate medical attention.
Listeria Symptoms in Pregnant Women and Newborns
Pregnant women are particularly vulnerable to Listeria infection and are approximately 10 times more likely to become infected than the general population. While symptoms may be mild in pregnant women, they can have serious effects on the fetus.
Listeria Symptoms in Pregnant Women
When pregnant women become infected with Listeria, they may experience:
- Fever and chills: Flu-like symptoms with elevated body temperature.
- Muscle aches and fatigue: Muscle pain throughout the body and severe fatigue.
- Mild gastrointestinal symptoms: Some pregnant women may experience mild diarrhea or abdominal pain.
Even if symptoms appear mild in pregnant women, they can have serious consequences for the fetus:
- Miscarriage: Increased risk of miscarriage if infected in early pregnancy.
- Stillbirth: Risk of stillbirth if infected in late pregnancy.
- Premature birth: Delivery may be induced earlier than the normal pregnancy term.
- Neonatal infection: Listeria can be transmitted to the fetus during delivery.
Listeria Symptoms in Newborns
Newborns infected during or shortly after birth may show the following symptoms:
- Fever: Abnormal rise in body temperature.
- Rash: Skin rashes may appear.
- Vomiting: May occur after feeding.
- Decreased appetite: Refusal to feed or decreased appetite.
- Breathing difficulties: In severe cases, respiratory distress may occur.
- Severe cases of meningitis or sepsis: Life-threatening conditions requiring immediate intervention.
Neonatal listeriosis has a very high mortality rate of up to 50%, necessitating immediate medical intervention.
Who is at High Risk?
While Listeria infection can occur in anyone, the following high-risk groups are more likely to develop severe symptoms and complications:
Pregnant Women and Fetuses
As mentioned earlier, pregnant women are particularly vulnerable to Listeria infection, which can severely impact the fetus. Listeria infection during pregnancy can cause miscarriage, stillbirth, premature birth, and life-threatening infection in newborns.
Adults Over 65
Elderly individuals have weakened immune systems, making them more susceptible to Listeria infection. They also have a higher risk of developing invasive listeriosis, which can be fatal.
People with Weakened Immune Systems
People with the following conditions have weakened immunity, increasing their risk of Listeria infection:
- HIV/AIDS patients
- Cancer patients, especially those undergoing chemotherapy
- Organ transplant recipients taking immunosuppressive medications
- Diabetic patients
- Those with chronic conditions like cirrhosis, asthma, ulcerative colitis
- People taking long-term immunosuppressive medications like steroids
These high-risk groups may experience more severe symptoms than typical Listeria infections and have a higher risk of developing complications like sepsis and meningitis.
How Does Listeria Infection Occur?
The primary route of Listeria infection is through consuming contaminated food. Listeria bacteria can be found in various foods and are particularly dangerous because they can survive and multiply at refrigeration temperatures.
Main Infection Routes
The main routes of Listeria infection include:
- Consuming contaminated food: The most common route of infection is eating food contaminated with the bacteria.
- Cross-contamination: Bacteria can transfer from contaminated food or utensils to other foods.
- Fetal transmission during pregnancy: If a pregnant woman becomes infected, the bacteria can be transmitted to the fetus through the placenta.
Foods with High Risk of Listeria
The following foods have a relatively high risk of Listeria contamination:
- Soft cheeses: Feta, Brie, Camembert, blue cheese, etc.
- Unpasteurized milk and dairy products made from it
- Ready-to-eat foods: Deli salads, refrigerated spreads, seafood salads, etc.
- Ready-to-eat meats: Hot dogs, sausages, pastrami, lunch meat, etc.
- Smoked seafood: Smoked salmon, smoked shellfish, etc.
- Ready-to-eat vegetables: Pre-washed salads, sprouts, etc.
- Fruits: Especially melons and apples that are eaten without peeling
People in high-risk groups should be particularly careful when consuming these foods and, when possible, heat them thoroughly before consumption.
How Long is the Incubation Period for Listeria Infection?
The incubation period for Listeria infection is considerably longer than for other foodborne pathogens, making it difficult to trace the source of infection in many cases.
Incubation period after Listeria infection before symptoms appear:
- Common gastrointestinal symptoms: Symptoms may appear about 12 hours after food consumption.
- Invasive listeriosis: Can have a very long incubation period of 1-6 weeks.
- Minimum-maximum incubation period: In some cases, symptoms may appear on the same day, while in others, the incubation period can last up to 70 days.
Due to this long incubation period, it's often difficult to identify the source of infection, and symptoms may appear after all the contaminated food has been consumed.
How is Listeria Infection Diagnosed and Treated?
Diagnostic Methods
If Listeria infection is suspected, diagnosis is made through the following methods:
- Clinical symptom assessment: Doctors comprehensively evaluate the patient's symptoms, medical history, dietary history, etc.
- Blood tests: Blood culture tests are conducted to confirm Listeria infection.
- Cerebrospinal fluid tests: If meningitis is suspected, cerebrospinal fluid culture tests are performed.
- Stool tests: Stool culture tests may be conducted if gastrointestinal symptoms are present.
- Other fluid tests: Culture tests of other bodily fluids may be performed as needed.
Confirmation is possible if Listeria bacteria are detected through these tests.
Treatment Methods
Once Listeria infection is confirmed, treatment includes:
- Antibiotic therapy: The main treatment for Listeria infection, using antibiotics like ampicillin and gentamicin.
- Symptomatic treatment: Concurrent treatment for symptoms like fever and dehydration.
- Hospitalization: Severe symptoms or high-risk individuals may require hospitalization.
- Long-term antibiotic administration: Invasive listeriosis may require 2-6 weeks of antibiotic treatment.
Early diagnosis and appropriate antibiotic treatment can greatly improve the prognosis of Listeria infection, so it's important to visit a medical facility promptly if suspicious symptoms occur.
How Can Listeria Infection Be Prevented?
To prevent Listeria infection, it's important to follow these food safety guidelines:
Precautions When Purchasing and Storing Food
- Check expiration dates: Check the expiration dates of all foods and don't consume expired products.
- Maintain proper temperature: Keep refrigerator temperature below 4°C and freezer temperature below -18°C.
- Separate food storage: Store raw meat, seafood, vegetables, etc. separately to prevent cross-contamination.
- Check freshness: Check the freshness of food before purchase and avoid suspicious products.
Precautions When Preparing Food
- Thorough cooking: Cook meat and seafood until the internal temperature reaches at least 75°C.
- Caution with ready-to-eat foods: Consume ready-to-eat foods as soon as possible after purchase.
- Wash vegetables: Thoroughly wash vegetables and fruits that will be consumed raw.
- Separate cooking utensils: Use separate utensils for raw and cooked foods.
- Hand washing: Wash hands with soap for at least 20 seconds before and after food preparation.
Special Precautions for High-Risk Groups
High-risk individuals (pregnant women, the elderly, immunocompromised) should avoid the following foods:
- Unpasteurized milk and cheeses made from it
- Smoked or raw seafood
- Ready-to-eat deli meats (unheated)
- Pre-washed salads and sprouts
- Refrigerated pâtés or meat spreads
If these foods must be consumed, it's safer to heat them thoroughly before consumption.
Recent Trends in Listeria Infection
According to recent reports from the CDC, food recalls related to Listeria infection continue to occur regularly. In 2024 and 2025, Listeria infection cases were reported in various foods, including ready-to-eat meat products, cheese, fruit, and supplement drinks.
A notable point is that Listeria infections sometimes occur in clusters in medical facilities or long-term care facilities, highlighting the importance of food safety management in facilities where immunocompromised patients live in groups.
Additionally, the fact that Listeria bacteria can survive and multiply in refrigerated environments continues to emphasize the risk of infection through refrigerated ready-to-eat foods.
Conclusion: Recognizing Listeria Symptoms and Preventing Safely
Listeria infection initially presents with general food poisoning symptoms like fever, muscle aches, vomiting, and diarrhea, but in high-risk groups, it can progress to serious complications like meningitis and sepsis.
Pregnant women, the elderly, and people with weakened immune systems are particularly vulnerable to Listeria infection, requiring special attention in food selection and preparation. Safe food storage and cooking habits can significantly reduce the risk of Listeria infection.
If suspicious symptoms occur, especially in high-risk individuals, it's important to visit a medical facility promptly for proper diagnosis and treatment. While Listeria infection can have a good prognosis with early and appropriate treatment, delayed treatment can lead to serious complications or death, making symptom recognition and early response crucial.
Small precautions and practices in daily life can protect our family's health from foodborne infectious diseases like Listeria. Take a moment now to check your kitchen and refrigerator, and practice safe food management habits.
