Reviewed By: Pramod Kerkar, MD, FFARCSI

Listeria infection or Listeriosis is a serious disease caused by consuming food contaminated with the bacterium Listeria Monocytogenes. It has recently been recognized as a major public health problem both in the United States and throughout the world. This disease affects mainly pregnant women, newborns, and adults with the weakened immune system. It can be avoided by following some simple recommendations.

Where Does Listeria Come From?

How does listeria monocytogenes enter into food? Listeria monocytogenes is widely distributed in the environment, found in soil water, the plants become contaminated directly by the soil or simply from manure used as fertilizer. It is present in healthy animals (especially cattle, sheep and poultry), they can carry the bacteria without appearing sick before our eyes and can contaminate foods of animal origin such as meats and dairy products. It is also present in the sewage system, vegetation, and plant material, water from trees, forage conserved in silos, and in man. It is believed that 5% of the human populations are carriers, but the percentage is much higher in particular groups, such as slaughterhouse workers.

The abundance of this bacterium in nature indicates that Listeria monocytogenes can be present in a wide variety of fresh and processed foods, including milk as is the case of unpasteurized (raw) milk or foods made from it as fresh (soft) cheese, bacteria can also contain meat products (especially raw meat products or uncooked derivatives such as cuts of cured meats in refrigerated and Viennese cabinets), birds and their products, vegetable products such as salads and seafood such as fish and seafood.

Listeria monocytogenes is destroyed by pasteurization and by heat processes such as those used to prepare pre-cooked meats, these must be sufficient to kill the bacteria; however, if industrial practices are not good, contamination may occur after processing.

How Long Does It Last?

At this time, there is evidence that low numbers of Listeria monocytogenes in a food can cause Listeriosis, but it is thought that fewer than 1000 organisms can cause disease in susceptible people.

Normally, this microorganism proliferates to potentially dangerous numbers within 1 to 35 days. The incubation period has been known and has a wide range from 1 to 91 days; however, under the ideal conditions it has been reported that they take less time (1 to 2 hours).

Serious infections can cause septicemia (blood poisoning), meningitis, encephalitis, infection of the central nervous system, and possibly death. These symptoms may be preceded by gastrointestinal symptoms such as nausea, vomiting and diarrhea, fever or head.

Pregnant women may experience mild flu with its symptoms such as chills, fever, and mild back pain. It can also lead to spontaneous abortion, premature birth, and mental retardation in the baby. Exposure to the bacteria does not always result in illness.

How is Listeriosis Acquired?

Listeriosis is contracted by consuming foods contaminated with Listeria Monocytogenes.

Babies can be born with Listeriosis if their mothers eat contaminated food during pregnancy. Although healthy people can consume contaminated food without getting sick, they have an increased risk of infection and can contract Listeriosis, probably returning to eating contaminated foods with even a small number of bacteria. People at risk can prevent infection with Listeria monocytogenes by avoiding certain high-risk foods and by handling food properly.

Can The Disease be Controlled?

Since this bacterium is widely distributed in nature, Listeria monocytogenes has become a threat in food production and processing environments. It can be established on surfaces that are in contact with food or man. However, good industrial practices and proper management at all stages of the food chain, including production, processing, warehousing, decommissioning services, and household environments, can minimize the impact of this pathogen.


Listeria monocytogenes is distributed in the environment, and as it was mentioned, this can contaminate certain type of foods. If they are ingested, these bacteria are able to enter the body and trigger the disease. The duration of the disease it-self will relatively depend exclusively on the host´s immune system and its capacity to kill bacteria.

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Pramod Kerkar

Written, Edited or Reviewed By:


Pain Assist Inc.

Last Modified On: September 17, 2018

This article does not provide medical advice. See disclaimer

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