Listeriosis: Understanding the Risks and Prevention

December 27, 2024

Listeria or listeriosis is a rare, food-borne disease caused by the bacteria Listeria monocytogenes. Humans acquire the disease by ingesting food contaminated with bacteria. The disease usually causes flu-like symptoms (headache, fever, chills, and body aches). However, it can lead to serious consequences in pregnant women, affecting both the mother and the infant. Additionally, older people (above 65) and individuals with weak immunity are prone to falling prey to the severe effects of the sickness. According to the WHO, listeriosis has a global prevalence of 0.1-10 cases per one million per year.¹ Even though the prevalence is low, the high mortality rate of the disease is a major concern. As per a systematic review, listeria monocytogenes infection was responsible for 23,150 illnesses and a whopping 5463 deaths.² Doctors usually prescribe antibiotics to treat the infection. You can keep the infection at bay by adopting good hand-washing habits and properly cooking your food.

Listeriosis Symptoms

Listeriosis sets after an incubation period of a few days. This period can range from 3 to 70 days. The median incubation period of pregnancy-associated listeriosis was found to be 27.5 days (17-67 days).³ So, it may take some time (for symptoms to appear) after eating contaminated food. As already mentioned, listeriosis can present with a range of manifestations, i.e., from manageable symptoms to life-threatening conditions.

Common Symptoms:

Fever & Chills

The intensity of the symptoms depends on the extent of organ involvement. Non-invasive infections present with fever, chills, and gastric symptoms like nausea, vomiting, etc.⁴ Moderate-grade fever (100℉) is seen in the majority of cases.

Gastric Symptoms

Pathologists identify Listeria as an enteroinvasive GIT pathogen. The most common symptoms of the disorder include nausea, vomiting, watery diarrhea, and headaches.⁵ Experts suggest clinicians take extra caution when diarrhea and flu-like symptoms are present in pregnant patients, as it may point toward life-threatening listeria infection.⁶

Body Aches

In most cases, muscle pains accompany gastric symptoms. Patients are often disturbed with multiple aching joints, fever, and gastric upsets. The febrile illness mostly presents with body aches (especially during pregnancy).

Neurological Issues:

Neurological symptoms develop when the infection spreads to the nervous system. Patients experience the following symptoms:

Confusion

Individuals report having an altered state of mind some days after eating contaminated food. Confusion is a feature of listeria infection.

Loss of Balance

Studies have revealed neurological abruptions in patients. Sheeps infected with the bacterium have a hard time balancing their bodies. Loss of balance and seizures in pregnant women can have grave consequences for the mother and the child.⁷

Convulsions & Seizures

Involvement of the nervous system can lead to convulsions and seizures. Mostly, these symptoms indicate serious consequences, such as meningitis/encephalitis.

Neck Stiffness

Severe invasive Listeria infection lays the foundation for meningitis (inflammation of the brain layers). You must get immediate medical attention if you are experiencing confusion, seizures, neck stiffness, etc.⁸

Headaches

Many patients present with isolated headaches due to underlying Listeria infection. The onset of headache is mostly attributed to listeria-induced meningitis.⁹ Headaches, convulsions, and seizures are mostly due to neurological involvement.

Symptoms During Pregnancy And In Infants:

The Listeria bacteria can colonize the birth canal; therefore, infants may get infected while passing through it (during birth). In addition to the flu-like symptoms and fatigue, pregnant women may experience the following symptoms of listeriosis:

Breathing Difficulties

When Listeria monocytogenes bacteria access the circulatory systems, they spread to different organs, causing sepsis, fever, and breathing difficulties.¹⁰ Both mothers and infants can suffer from breathing abnormalities (but infants are at greater risk of breathing problems). In a 35-year-old pregnant lady, the baby acquired a listeria infection and showed signs of impaired breathing while the mother’s breathing was normal.¹¹ Seizures and skin rashes may accompany breathing difficulties in newborns.

Miscarriage

Listeria infection is notorious for causing miscarriages. The Gram-positive bacteria can potentially lead to issues like congenital neonatal infections, preterm births, miscarriages, etc.¹² In a clinical study of women with miscarriages, specimens of 33.5% of subjects were positive for Listeria species.¹³

Premature Birth & StillBirth

Researchers have found a strong connection between Listeria infection and premature births. In a study, placental swabs were taken from women with early premature births. The findings revealed that almost 40% of abnormal births were caused by listeria infestation. The highest rate of listeria-induced premature birth was found in 26-35 year old women.¹⁴
Listeriosis also contributes to preterm labor, fetal loss, and stillbirth. Clinical studies reveal that listeria-induced stillbirth occurs secondary to maternal chorioamnionitis.¹⁵
Newborns suffering from bacterial infection are not interested in accepting food/milk and are often seen crying constantly. Fever and vomiting are also common. Diseased infants have breathing difficulties, too, which can be a serious concern. Therefore, infants and pregnant females need emergency symptomatic management and treatment with antibiotics.

Complications Of Listeria

Listeriosis has fatal consequences if it infests the nervous system. The bacteria can cross the blood-brain barrier and lead to severe complications (especially in immunocompromised patients)¹⁶ which are mentioned below:

Brain imaging of a patient reveals rhomboencephalitis in a patient suffering from Listeriosis (A-E). Image courtesy of PubMed available under CC by 4.0.

Meningitis And Sepsis

Meningitis refers to swelling of the brain layers (meninges) that can prove to be fatal. Listeria monocytogenes-induced meningoencephalitis is rare, but it progresses rapidly. It is often associated with other serious complications such as hydrocephalus, cerebral palsy, and brain abscesses. Thus, it has a high mortality rate.¹⁷ Listeria monocytogenes is a rare cause of meningitis and septicemia in liver cirrhosis patients.¹⁸ Patients present with high-grade fever, headaches, neck stiffness, sleepiness, sensitivity to light, loss of consciousness, etc.

Encephalitis

Inflammation of the brain cells (encephalitis) has adverse effects. Listeria monocytogenes-associated encephalitis is a severe condition that can be fatal for immunocompromised patients. This particular complication may be associated with other brain anomalies like abscesses.¹⁹ Quick diagnosis and timely treatment are necessary in brainstem encephalitis patients.²⁰

Listeriosis Causes

Listeria is caused by the bacteria Listeria monocytogenes. The pathogen gains entry into the body after you eat food contaminated with it. Identifying contaminated food is difficult because, unlike other microbes, food affected with listeria doesn’t taste or smell bad (rotten).

What Foods Carry Listeria Bacteria?

The germs of Listeria are highly prevalent in nature. You can find the bacteria in soil and groundwater. As it is a zoonotic infection, Listeria monocytogenes is present in animal feces (from where it can get transmitted to humans). The following edible items can serve as sources of listeria monocytogenes:

Hot Dogs & Deli Meats

Investigations reveal that Listeria monocytogenes is a stubborn bacterium that survives even in harsh environments. A study found that instead of falling, the number of bacteria in hot dog sausages increased when kept at 7-10℃. However, the growth rate became steady (but did not decline) even at freezing temperatures, i.e., 10℃!²¹ Improperly cooked food is an important source of disease-causing bacteria.²²

Vegetables & Fruits

Ready-to-eat vegetable salads can serve as sources of L. monocytogenes. The bacteria can survive and grow even at low temperatures (4-10℃). Some veggies like purple cabbage, beetroot, and carrots did not support bacterial growth.²³ Fresh-cut melons can prove to be breeding grounds for the bacteria.²⁴
Therefore, there is a need to adopt biopreservation approaches to reduce bacteria count in fresh vegetables.²⁵ Unpasteurized dairy items and juices can also make you sick.

Risk Groups

Pregnant women and individuals with weak immune systems are prone to developing severe forms of infection. Chronic disorders such as AIDS, cancer, hepatitis, and end-stage renal disease weaken the immune system. Moreover, auto-immune and transplant patients on immunosuppressant drugs must also stay vigilant about listeriosis infection.
End-stage renal disease patients are severely immunocompromised and most prone to developing severe listeria infection.²⁶

Is Listeriosis Contagious?

Listeria is transmissible but not contagious. Infected pregnant mothers can transfer the pathogen to the fetus (through the placenta). However, you can not transmit it to another person.

Listeriosis Diagnosis

History:

Your doctor will take a complete history of the start of symptoms (gastric upset, headache, convulsions, etc.) and may ask if you consumed any unpasteurized milk or undercooked meat. If suspected, your doctor may order an array of diagnostic tests.

Diagnostic Tests:

Blood Test

Pathologists check the presence of the L. monocytogenes bacteria in the blood using a method called mass spectrometry. This method rapidly and accurately identifies the pathogen and is therefore, frequently used as a diagnostic test in pregnant women.²⁷

Placenta

For PCR testing, fluid can be withdrawn from vessels or the placenta (in pregnant women).²⁸

Cerebrospinal fluid (CSF)

If meningitis/encephalitis symptoms are present, your doctor may collect a small amount of CSF (as a sample). The number of bacteria in the cerebrospinal fluid is usually small. Thus, pathologists use a special real-time PCR assay to detect L. monocytogenes DNA.²⁹

Meconium (in infants)

An infected infant’s first green-colored poop can tell about the underlying serious infection. Listeriosis-affected children may deliver meconium before birth, i.e., inside the womb. Therefore, meconium-stained amniotic fluid may indicate early onset Listeria in newborns.

Listeriosis Treatment

For mild symptoms, your doctor may not advise you on any drugs. Instead, you should just take ample rest and stay hydrated (by drinking plenty of fluids). Listeriosis medication is only indicated in moderate-to-severe disease.
Antibiotic therapy is the mainstay of listeriosis treatment. Doctors lay special emphasis on pregnant ladies, patients with weak immune systems, and old adults (above 65). The most prevalent antibiotics for listeria include ampicillin and sulfamethoxazole.
During the COVID-19 pandemic, listeria developed secondary to the SARS-CoV-2 infection. In these cases, a combination of intravenous ampicillin, sulfamethoxazole, and meropenem greatly improved symptoms of bacterial meningitis.³⁰ Early detection of the disease is crucial in neonates because of its high mortality rate. Your health provider will quickly administer drugs after birth. Ampicillin is the first-line therapy in neonatal listeriosis as well.³¹
A new retrospective study advocated gentamicin and ampicillin combination therapy in cases of invasive listeriosis. This particular therapy effectively reduces the 90-day mortality among patients with invasive listeriosis.³²

Listeriosis Prevention

Listeria monocytogenes can survive even in the harshest environments. Therefore, prevention is an arduous task. However, pregnant women and immunocompromised individuals can adopt these precautionary measures to minimize the risk of invasive infection:

Properly cook deli meats and hot dogs. Experts suggest cooking the meat to an internal temperature of 165℉. Only this much heat can kill the pathogenic bacteria.
Wash your hands before consuming and cooking food.
Thoroughly wash all veggies and fruits before eating.
Avoid unpasteurized dairy items and juices.
Use canned foods (meat), avoid refrigerated food items, and minimize intake of leftovers.
Properly cover/wrap all your food items (especially raw meat) when storing them in the refrigerator.

Final Word

Listeriosis/Listeria is a rare bacterial infection caused by ingesting the Listeria monocytogenes bacteria. In most cases, it causes mild febrile disease with nausea, vomiting, headaches, diarrhea, etc. However, in pregnant women, infants, and immunocompromised patients, it may take an invasive form, leading to severe consequences. While in weak, older adults, it may cause meningitis, encephalitis, and sepsis, the disease can lead to issues like stillbirth, premature labor, miscarriages, etc. in pregnant women. It has a high mortality rate. Thus, immediate treatment is indicated for neonatal listeriosis. PCR test of blood samples reveals bacterial DNA.
The bacteria may get into your food from soil, groundwater, and animal feces. Once inside the edible items (veggies, meat, and unpasteurized milk), it is hard to destroy. Thus, you should properly cook meat and wash veggies/fruits before eating. Antibiotics like ampicillin and sulfamethoxazole are effective against L. monocytogenes and show quick results.

Refrences

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