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Listeria Infection: Symptoms, Causes and the Dangers It May Pose

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listeria

Story at-a-glance -

  • Listeria infections, which affect more than 1,000 patients per year, stem from improper food handling and storage
  • It may contaminate foods if they are incorrectly stored or if ready-to-eat foods are exposed to contaminated materials or utensils used to prepare uncooked food
  • Learn more about this condition, its causes, symptoms and treatment options

While sanitation has been improving over the years as more and more information is found on foodborne diseases, millions of people still contract illnesses from wrongly prepared food products, be it from contaminated preparations or incorrect storage. One of the possible conditions is listeria infection, which is caused by the listeria monocytogenes bacterium.

While listeria infections are rare and do not affect a considerable number of the population, it is especially dangerous for pregnant women and immunocompromised individuals, such as the elderly. This article will primarily focus on what listeria is, its symptoms, causes and possible treatment options.

What Is Listeria Infection?

Listeria monocytogenes bacteria are abundant in numerous organic materials, such as soil, spoiling vegetation and animal manure. Once they come into contact with food and are consumed, these bacteria may cause considerable discomfort and even dangerous complications.1

Through evolution, listeria monocytogenes managed to develop a process that allows it to penetrate cell membranes and spread from cell to cell. However, studies show that the process by which the bacteria are spread is extremely crucial. Once this method of proliferation develops inside the human body, the bacteria may attack the central nervous and digestive systems.2

While the primary infection caused by the bacteria is called listeriosis, other independent conditions can stem from this, which include meningitis, intrauterine infection and encephalitis.3 It is often contracted from wrongly processed meats and animal products, as well as contaminated food crops. According to the U.S. Centers for Disease Control and Prevention, at least 1,600 Americans get listeriosis every year, with about 260 patients eventually succumbing to the condition.4

But even if large numbers of people are exposed to the bacteria, only a few may start showing symptoms. These symptoms, however, fall under the "bimodal distribution of severity." This means that these infections either manifest as mild or severe — only in the extremes.5

Notable Listeria Infection Outbreaks

Outbreaks often occur when two or more people become infected by a foodborne disease from a specific food product. A serious listeria outbreak in the U.S. happened in 2011, stemming from contaminated cantaloupes from Jensen Farms.

While it is regarded as one of the worst outbreaks, infecting 147 people and causing 33 confirmed deaths,6 the worst outbreak in the world was in Africa in 2018, killing 189 people and sickening 982 as of March 2018. About 43 percent of the deaths were newborns infected during gestation, The New York Times said. This outbreak was traced to processed bologna.7

While the cause for the Jensen Farms outbreak is unclear, one of the purported origins was due to a dump truck used to transport cantaloupes to a cattle operation, which eventually contaminated the whole facility.8

The increase in fresh food cases of listeriosis, such as in the cantaloupe recall, shows that listeria infections are not limited to processed, refrigerated or unpasteurized foods. The hygiene in fruit and vegetable propagation may play a role in the massive number of listeria cases.

The most recent listeria outbreak that has affected Austria, Denmark, Finland, Sweden and the United Kingdom is actually ongoing. The reason for the outbreak was first traced to frozen corn, but it has since been found to be caused by other types of frozen vegetables. While the recalls have been set, the risk for listeria infections are still present until all the products are removed from the shelves.9

Is Raw Milk Undeservingly Demonized Because of Listeria Scares?

Raw milk is often one of the first food products that figure in the listeria warnings issued by the CDC. This is often accompanied by recommendations that pasteurized milk is the only dairy product safe for human consumption, as it supposedly removes all the risks of bacterial growth. Of course, these recommendations also leave out the fact that pasteurization kills off most of the beneficial enzymes and nutrients found in raw milk.

Aside from that, the warnings against raw milk are blown out of proportion in favor of pasteurized milk, and they also fail to say that the risk of getting a listeria infection in raw milk is almost equal to the risk in pasteurized milk, as these products may still be contaminated through improper handling.10 It all just boils down to the source and storage.

The problem is that most consumers are unaware that there are basically two types of raw milk. CAFO (concentrated animal feeding operations) raw milk is the type of milk specifically produced to be put through the pasteurization process.

Quality control is incredibly lenient in this regard, as the milk goes through extremely harsh processes, to ensure that all types of bacteria are killed off. The second type is raw milk from pasture-raised cows and is required to reach strict standards to ensure safety and quality.11

This bias is appropriately put on display in the 2015 listeria outbreak caused by contaminated batches of Blue Bell Creameries ice cream. Today, Blue Bell Creameries is back in business after the deadly outbreak, while small organic farms are forced to close down operations completely after causing alleged "outbreaks."12

In fact, the Weston A. Price Foundation notes that the U.S. Food and Drug Administration (FDA) has attacked raw milk despite the absence of concrete proof that it has caused listeria outbreaks in the population in the past 40 years or so.13

3 Listeria Infection Symptoms to Look Out For

In non-pregnant individuals, a listeria infection may manifest in different ways, depending on the severity and the spread of the bacteria in the body. Because of the numerous conditions that may arise due to underlying listeriosis, the presence of the following problems may point to this infection:14

  • Febrile gastroenteritis — Listeria may cause gastroenteritis, a noninvasive syndrome. Some of its signs include diarrhea, fever, chills, abdominal pain and nausea.
  • Bacteremia — This refers to the presence of bacteria in the blood. Fever, a rapid heart rate and chills usually accompany this condition.
  • MeningitisIf the listeria bacteria reach the brain, symptoms like muscle aches, a stiff neck, loss of balance and confusion may arise.

If you start to suffer the symptoms above, seek medical help as soon as possible. This will help contain the infection and limit its spread to other systems in the body. This is especially important if you start suffering from psychological and cognitive function problems.

Listeria Infection Symptoms in Infants

While it is important that you remain vigilant of these symptoms at all times, the importance doubles when you're pregnant as it may endanger you and your child.15 There are two types of listeria infections in infants, and they differ depending on the onset of the condition: early-onset and late-onset.

Early-onset listeriosis is usually acquired from the mother, with the infant typically being diagnosed with sepsis within the 24 hours after birth. The cause of late-onset neonatal listeriosis, on the other hand, is unclear and may be because of external factors — it occurs rarely. Some of the symptoms of late-onset listeriosis may not be as straightforward as you'd want them to be, but they include:16

  • Irritability
  • Poor feeding
  • Fever

What Causes Listeria Infection?

Listeria monocytogenes is a pathogenic bacterium that commonly thrives in water, soil and some poultry and livestock products. Compared to other bacteria, listeria monocytogenes is much more resilient, surviving even in refrigerated or frozen conditions. The only surefire ways to remove this bacterium from food products is through cooking and pasteurization.17

If you're not entirely sure what types of foods you should be avoiding or limiting your intake of to drastically lower your risk of a listeria infection, here's a list:18

  • Ready-to-eat meats and hotdogs
  • Refrigerated meat spreads
  • Dairy products from untrustworthy sources
  • Refrigerated smoked seafood
  • Uncooked sprouts

Fresh vegetables and fruits may also cause listeria infections, especially if left unwashed. This is due to the possible contact between the fresh produce and animal manure, which is sometimes used in farming, and can contaminate groundwater sources like rivers and irrigation ditches used on the produce.

Listeria in Pregnancy

While listeria infection usually goes away on its own, this does not mean that it should be ignored in hopes that it will resolve on its own. This is especially important when you get listeriosis during pregnancy, as this opens you up to numerous dangerous side effects and complications. Pregnant women are especially susceptible to listeria infection because the hormone changes happening in their body may compromise their immune system.19

4 Possible Pregnancy Complications That May Arise Due to Listeria Infection

Pregnant women are 20 times more susceptible to this infection, which exposes them to a handful of dangerous complications in both their health and their unborn child's, with the child's being more severe.20 Some of the most common complications that pregnant women can suffer from include:

  • Stillbirths — One documented case of listeria infection causing a stillbirth was thoroughly discussed in the 1966 volume of the Journal of Clinical Pathology. In this specific case, the listeria infection was not apparent in the mother, aside for a slight fever. However, the stillborn child showed numerous evidence pointing to widespread listeria infection, which affected the lungs, spleen and liver.21
  • Miscarriages — The listeria bacteria can alter the placenta's ability to protect the unborn child. This may weaken both the fetus and the mother's reproductive tract, leading to miscarriages early in the pregnancy.22
  • Preterm labor — In a 1993 study in the Zeitschrift fur Geburtshilfe und Perinatologie, scientists found that seven strains of the bacteria had the ability to induce uterine contractions, increasing the risk of premature birth.23
  • Death of newborn — If the listeria infection occurs late into the pregnancy, there is a chance that the symptoms will start appearing in the child upon birth, usually starting with symptoms of meningitis. About 60 percent of babies with infected mothers are born premature. They typically start showing signs within 24 hours. Unfortunately, 20 to 60 percent of these neonatal cases die because of the infection.24

Listeria in the Elderly

Because of their compromised immune system function, caused by either old age or other external factors, the elderly are at a higher risk of suffering from listeriosis. In fact, more than half of the patients who suffer from listeriosis belong to the elderly population.25

In 2009, a rise in listeria infections amongst pensioners and the older generation was observed with the reason being that they were more likely to ignore the use-by dates on the packaging of their food products. In fact, a survey found that approximately 40 percent of the elderly population would knowingly eat dairy products up to three days past the use-by date.26 Their weaker immune system puts them at a higher risk of being more severely affected by the bacteria.

Listeria Treatment: How Can This Infection Be Treated?

Listeria infection treatment largely depends on the severity of the symptoms and the immune strength of the patient. In mild cases, treatment is not required, as the symptoms usually go away on their own. In fact, healthy children, teenagers and adults don't require any type of treatment as their immune systems are efficient enough.

However, because of the risks that listeriosis poses on pregnant women, the elderly and immunosuppressed, these patients often require immediate treatment. While the conventional medical route when it comes to listeria infections is through antibiotics, there are also natural ways that you can help your body recover, such as:

  • Ingest garlic shoot juice — A 2006 study found that a 5 percent concentration of garlic shoot juice had an inhibitory effect on Listeria monocytogenes proliferation. Under the microscope, lysis of both the cytoplasm and cell wall in the bacteria was observed.27
  • Stay hydrated — It's important that you replenish your body's fluid levels to avoid dehydration, as vomiting and diarrhea usually accompany listeriosis. This will help your body recuperate much faster as it will not need to compensate for dehydration. Aside from drinking water, you can try sucking on some ice chips or sipping bone broth.28

Some of the most common antibiotics prescribed for this infection are:

  • Ampicillin is often prescribed alone or in conjunction with other antibiotics, including gentamicin. This antibiotic mainly works by rendering the bacteria unable to create an effective cell wall, eventually leading to their death.29
  • Gentamicin, which is usually administered through injections, is an antibiotic that targets various types of bacteria by inhibiting protein production. This eventually messes up the bacteria's overall processes they need to survive.30

While antibiotics may be the conventional route for the treatment of listeria, it's important that you are aware of the numerous risks of side effects that they pose. In mild cases, antibiotics may cause nausea, vomiting, diarrhea and fever. In severe cases, they may cause allergic reactions and anaphylactic shock, which may lead to death.31

If it is absolutely necessary for you to take antibiotics, you can help your body maintain balance by taking probiotics or sporebiotics, which will keep the good bacteria in your gut balanced, as antibiotics cannot differentiate between good and bad bacteria. If you're not familiar with sporebiotic supplements, these are made up of bacillus spores and may help reestablish the gut microbiome and enhance your overall immune function.

Listeria Treatment for Pregnant Mothers

Because of pregnant women's sensitive condition, listeriosis treatment during pregnancy is essential to ensure both the safety of the mother and unborn child. During the onset of the infection, listeriosis may cause vomiting and diarrhea, which may cause excessive loss of water from the body, leading to dehydration. This may cause weakness and other health repercussions.32

If a pregnant woman starts showing signs and symptoms of listeriosis, treatment and testing are often given simultaneously to deal with the presumptive infection as soon as possible. Listeria diagnosis usually consists of blood tests and a placental culture in the event of a delivery. If the tests come back negative, thorough evaluation should be done to determine whether the antibiotics prescribed should be continued for safety.33

Listeria Prevention

Like other infections that stem from food contamination, listeria prevention mainly depends on hygiene and the quality of the food that you are ingesting. While listeria infections may be rare, this does not mean that you can ignore caution and expose yourself to the risk of contracting an infection. To make it easier for you, here are a few tips you can follow to drastically decrease your infection risk:34

  • Avoid drinking dairy products from untrusted sources — While health agencies vilify raw dairy products because they supposedly increase your risk of bacterial infections, the same agencies also fail to note that pasteurized dairy has almost the same risks of contamination with different strains of bacteria as raw dairy. When buying dairy products, it's important that you only get them from trustworthy sources to ensure you're getting the highest quality.
  • Wash utensils and kitchen tools used to handle raw or uncooked ingredients — Avoid interchangeably using utensils between raw foods that are going to be cooked with foods that are going to be eaten fresh.
  • Make sure to separate uncooked meats from vegetables, fruits and cooked foods — Properly storing your food inside the refrigerator may significantly reduce the risk of listeria from getting into foods that do not require cooking.
  • Thoroughly cook meats and other ingredients, and avoid consuming half-cooked or poorly cooked food — Make sure that all your meals are properly and sufficiently cooked, preferably in clean and hygienic environments.
  • Eat ready-to-eat foods immediately, avoiding prolonged exposure to air — While you might be tempted to leave your food unattended and get back to it when time permits, this is a surefire way for listeria bacteria to get into your food.

However, because of the unpredictable way that this type of bacteria spreads from food or other materials, it's important that you strengthen your immune system to combat this infection. Your body's immune response plays an important role in regulating the severity of the infection and its spread in your various systems. Immunocompromised patients manifest worse symptoms because the bacteria easily enter their bloodstream, leading to sepsis.

If you want to nip listeria at the root, you can start with strengthening your immune response through various natural practices, including:

  • If you smoke, stopIn a 2017 study from the Oncotarget journal, cigarette smoking was found to negatively affect innate and adaptive immunity, exposing you to a greater risk of infections, cancers and other diseases. Ironically, while smoking may weaken your immune system, it may also increase autoimmunity risk.35
  • Eat a healthy diet — Numerous vitamins and minerals play a direct role in promoting immune function, including vitamins A, C, D and zinc. Ensuring that your diet has plenty of these nutrients may help shield you or at least significantly reduce your risk of contracting different diseases and infections.36
  • Exercise regularly — Physical activity may influence the immune system as regular exercise was found to provide a certain protective effect. However, it's important that you know your limits as overexertion may lead to an opposite effect.37
  • Get adequate sleep — In a 2015 study from the Journal of Immunology Research, researchers noted that sleep influences the body's ability to fight off infections and other illnesses. They found that lack of sleep significantly dampens the body's immune function.38

4 Side Effects or Complications of Listeriosis

While the infection itself brings patients a handful of painful symptoms, listeriosis, if left undiagnosed and untreated, may also expose you to these complications:

  • Neonatal sepsis — In the event that the mother becomes infected prepartum, the unborn child is at high risk of suffering bacterial septicemia. This may cause respiratory distress, an enlarged liver and decreased muscle tone. The prompt diagnosis and treatment of this complication is crucial to decrease the risk of mortality.39
  • Meningitis — The Listeria monocytogenes bacterium is one of the leading causes of meningitis in the population, trailing behind Streptococcus pneumonia and Neisseria meningitides bacteria.40 Symptoms of meningitis include nausea, vomiting, sensitivity to light, muscle pain and confusion. In the later parts of the infection, patients may suffer from seizures and fall into a coma.41
  • Brain abscesses — While extremely rare, the listeria monocytogenes bacteria can cause brain abscesses. When the infection becomes widespread, it may reach the brain, allowing pus to accumulate in certain parts of the brain.42
  • Listerial endocarditis — In 7.5 percent of the cases of listeria infection, the bacteria manage to make their way to the heart. This causes inflammation in the heart tissue. About half of the patients who suffer from this end up dying.43

Frequently Asked Questions (FAQs) About Listeria Infection

Q: How common is listeria in pregnancy?

A: About 17 percent of pregnant women fall victim to listeria infections annually, exposing them to numerous risks.44

Q: How is listeria treated?

A: Conventional treatment for listeria is through antibiotics, such as gentamicin and ampicillin. However, these medications also come with numerous risks and side effects, including nausea, vomiting and dangerous allergic reactions. It's important to know that there are natural ways to combat this infection, including maintaining a good level of hydration and using garlic shoot juice.45

Q: How does listeria get into food?

A: Listeria may contaminate foods if they are incorrectly stored or if ready-to-eat foods are exposed to contaminated materials or utensils used to prepare uncooked food.

Q: How long does a listeria infection last?

A: The duration of a listeria infection depends on the severity and length of the incubation period. Symptoms of listeria may start to show up between two and 70 days after exposure. 

Q: Is listeria contagious?

A: Listeria is mainly contracted from contaminated food and water. It cannot be transmitted from person to person through proximity.

Q: How do you test for listeria?

A: A listeria infection may be diagnosed through various tests, including blood and spinal fluid. If a pregnant mother shows symptoms of listeriosis and there are no other subsequent conditions that may be causing them, testing and treatment may be given at the same time.

Q: How do you get listeria?

A: You can get listeria from a variety of sources, including contaminated ready-to-eat food products, refrigerated meats and dairy products. While the listeria bacterium is purely foodborne, transmission is possible between the mother and the unborn child.46

Q: How common is listeria?

A: Listeria is present in a lot of foods, specifically those stored in refrigerated environments, like deli meats and ready-to-eat sandwiches.

Q: What temperature kills listeria?

A: The listeria bacteria can be killed off in temperatures greater than 65 degrees Celsius or 149 degrees Fahrenheit.47

Q: Does cooking kill listeria?

A: Listeria is one of the hardest bacteria to kill because it cannot die in low or freezing temperatures. The good news is that listeria can be killed off by cooking, specifically in temperatures higher than 149 degrees Fahrenheit. But while cooking can kill it off, cooked food can be contaminated during storage.

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