Listeriosis (Listeria Bacteria Outbreak) Spread, Symptoms, Treatment

A potentially deadly outbreak of listeriosis in several states in the USA has led to a recall of frozen vegetables from a specific processing plant since April 2016. The initial recall was then expanded in May 2016 to 358 food products under 42 brands in the United States and Canada. This disease is relatively rare but outbreaks do occur and can be devastating when newborns, the elderly or people with weak immune systems are infected.

What is listeriosis?

Listeriosis is a disease caused by infection with the Listeria species of bacteria. It is mainly spread through contaminated food. The bacteria is highly resilient and can survive freezing. However, with adequate cooking the bacteria can be destroyed prior to consumption. Listeriosis can be effectively treated with antibiotics but most healthy people with mild symptoms will not even require treatment.

Death Rate of Listeriosis

Listeria infection affects 2 to 3 out of a million Americans every year. In newborns the infection can lead to death rates as high as 4 out of 10 infected babies. This drops to less than 10% in older children and adults. However, in the past few years the CDC has recored death rates as high as 21% related to listeria infection. Apart from newborns, pregnant women, the elderly and immune compromised individuals were at the greatest risk of fatalities.

Causes and Spread

Listeriosis is caused by the bacterium Listeria monocytogenes. It enters the human body when contaminated food ir water is consumed. Listeria bacteria are widely found on raw vegetables due to contaminated soil that it was grown in, undercooked meat and in unpasteurized milk. Processed foods such as deli meats and cheeses can also be contaminated and therefore spread the bacteria.

Once the bacteria enter the gut and if it is not neutralized by the immune system, it can then travel via the bloodstream to various sites in the body. Listeriosis usually results in meningitis in newborns. It can also lead to blood poisoning (sepsis). When the bacteria lodges in organs it is can cause tiny abscesses with destruction of healthy tissue. However, a healthy immune system is usually able to combat the bacteria quite effectively.

Read more on food and water safety.

Who is at risk of listeriosis?

Any person can become infected with listeriosis but the people who are more likely to experience a severe with complications include:

  • Newborn babies
  • Pregnant women
  • Elderly people
  • Immune compromised individuals like HIV/AIDS patients

Listeria Outbreaks

Listeria outbreaks are not uncommon but often does not gain significant media attention since the severity of the illness is limited in healthy people. It is important to understnd that listeriosis can be deadly and the infection should be taken seriously when it occurs in high risk groups. Not only is listeriosis easily treated, it can also be easily prevented with minor dietary and lifestyle changes.

Unpasteurized milk is not widely available so outbreaks are limited from this source. Similarly undercooked meat is a culinary choice and may not affect large populations at one time. However, it is common to consume fruit and vegetables raw or partially cooked. Recent outbreaks since 2009 have almost always involved fruits and vegetables. Contamination is usually from the soil and/or water used to grow and irrigate the fruit and vegetables (farm to fork transmission).

Processed foods have also been implicated in the transmission of Listeria. The contamination appears to arise between the cooking and packing stages when it comes to processed meat products like hot dogs and deli meats. Cheeses made from pasteurized milk have also been found to be contaminated and this usually arises during the cheese-making process.

Signs and Symptoms

It is possible to have a Listeria infection with little to no symptoms. It largely depends on individual immune defenses. Even when symptoms arise in healthy people, it is usually mild and resolves on its own within a few days. These signs and symptoms include:

  • Fever
  • Malaise
  • Muscle pain
  • Nausea
  • Diarrhea

A severe Listeria infection will result in sepsis and meningitis once the bacteria enters the bloodstrem and reaches the nervous system. These signs and symptoms include:

  • Stiff neck
  • Headache
  • Light sensitivity
  • Loss of balance
  • Irritability
  • Confusion
  • Seizures

There may also be fluctuating fever, difficulty breathing, vomiting, loss of appetite and skin rash noticed in infants.

Read more on meningitis.

When do listeriosis symptoms arise?

The first symptoms arises within a few days of consuming the contaminated food. However, it can arise as late as weeks or even a few months thereafter. In these instances it is often difficult to identify a possible source.

Treatment of Listeria

People who are otherwise healthy, not within the high risk group and have only mild symptoms do not always need medical treatment. However, other individuals will require antibiotic therapy. Newborn infections should be managed in a hospital and in severe cases ICU admission may be necessary for infants. The antibiotics used in treating listeriosis includes:

  • Ampicillin
  • Gentamicin
  • Sulfamethoxazole and trimethoprim
  • Penicillin G

The prognosis is very good when listeriosis treatment is started before complications like sepsis, menigitis or encephalitis arises. In severe or poorly managed cases, there is the risk of complications like hydrocephalus, mental retardation and even death.

Prevention of Listeriosis

Listeriosis can be prevented with simple dietary and lifestyle measures.  This includes:

  • Practice good hygiene at all times. Hand washing is extremely important especially when handling food and before meals. Cooking and eating utensils should be thoroughly cleaned before use. Cutting boards are a maor risk and boards used for preparing meat should not be used for vegetable preparation. Always clean boards thoroughly.
  • Raw vegetables and fruits must be thoroughly cleaned before consumption. Washing it under running water and scrubbing are effective but it can be further cleaned with sterilising fluids that are suitable for foods. Remember that even vegetables that are to be cooked should be thoroughly cleaned. Frozen vegetables can also be a risk as noticed in the 2016 outbreak.
  • Meat should be cooked thoroughly. Minimum cooking temperates vary between 140°F to 165°F and a short resting time of 2 to 3 minutes is advisable for beef and pork. Although processed meats are often not cooked and simply heated, where possible it should be cooked for at least a few minutes.
  • People who are considered to be high risk should avoid foods that are likely to carry Listeria bacteria, such as hotdogs, deli meats and soft cheeses. Avoid unpasteurized milk or related dairy products altogether.



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