Listeria: What It Is & The Food-Borne Illness It Causes

Listeria: What It Is & The Food-Borne Illness It Causes
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The key difference between this and a few other bacteria of its species is there is a type called monocytogenes (pronounced, maw-no-si-Taw-juh-neez) that not only causes disease in humans but, unlike other food-borne bacteria, it can grow in the refrigerator.

Opportunistic Pathogen

Listeria is known as an “opportunistic pathogen” and that means, it hangs around acting normal within the human body—maybe even in the intestines—until that body loses some of its protection or if the immune system and the ability to fight disease lowers, then listeriosis strikes.

Most healthy adults can be exposed with no risk. The body’s normal defense system against listeria is named cell-mediated immunity because lymphocytes or “T-cells” can fight it off. But even though it has been around for decades in soil and decaying vegetation, now every year it causes about 2,600 instances of severe illness.

Eating contaminated food is the link to illness, and listeriosis infection causes symptoms such as:

  • Fever and chills
  • Muscle aches
  • Nausea or vomiting
  • Diarrhea or other gastrointestinal—stomach related—symptoms

If it spreads to the less healthy human:

  • Headache
  • Stiff neck
  • Confusion
  • Loss of balance
  • Convulsions
  • Death

Few people with normal immune function go on to have the more severe, life-threatening forms of listeriosis; characterized by septic shock (body wide infection), meningitis (inflammation of the protective membranes covering the brain and spinal cord known as the meninges,) and encephalitis (infection of the brain tissue itself).

Early signs of listeriosis can generally be found in stool cultures. Machines like Magnetic-resonance Imaging (MRI) are used to confirm or rule out brain or brain stem involvement.

At Risk Foods and Groups

Listeria can be found in dairy products like ice cream and soft cheeses, hot dogs, deli meats, fish products, human and animal feces, and raw foods that have been contaminated or come in contact with the bacteria. The illness typically comes from eating the infected products.

If pregnant women ingest the bacteria they can lose their baby or it may result in a stillbirth or infection in the unborn child (as do many other diseases, unfortunately). Consequently young children and the elderly are also listeria targets because they are part of the “susceptible population,” as are people with AIDS or folks with diabetes, cancer or kidney disease. This is because their immune systems are either too young or decaying, so there is a higher death rate among these particular groups.

In a 2011 Listeria outbreak, the culprit carrying the disease happened to be cantaloupe.

Cantaloupe Danger

This particular cantaloupe outbreak in 2011 had more than one strain as identified on a database called PulseNet, kept by the Centers for Disease and Control (CDC)—a key investigative tool used by federal officials to locate the source of an outbreak. The cantaloupe contagion would eventually be found in twenty-eight states.

Since there are hundreds of strains of Listeria, two or more can sit side by side on the same food. In the end, five different deadly strains were linked to the Jensen family farm in Colorado, and that became the worst outbreak in a hundred years—on a produce that had never been known to foster Listeria—killing thirty-three people.

Jensen Farms

According to experts at the CDC, Jensen Farms had never been swab-tested by licensed examiner/inspectors. They produced cantaloupes, onions, carrots, watermelon and other food products.

In order to survive the food business, the Jensen brothers planted enough orange melons to supply dozens of states with three hundred thousand cases. Their washing and sorting machine on the farm was originally used to clean potatoes but had been adapted for the cantaloupes.


According to the Food and Drug Administration (FDA), cantaloupe and other melons made up 16 percent of all produce-related outbreaks in a twelve-year period.

“Cantaloupe has been problematical,” says David Gombas, senior vice president for food and safety and technology at the United Fresh Produce Association in Washington, D.C.

Those cool little pockets and crevices that are typical on the surface of cantaloupe have a tendency to hide bacteria in the crevices. So washing the surface is a plus, unless the cantaloupe is contaminated on the inside.

Regulators' Shortcomings

When regulators find problems in affected foods, they begin doing something about them. But after major food disasters when government entities have the opportunity to make a change for the future safety of consumers, they stop short. According to the authors of the book, Eating Dangerously, “Very few of the people and companies pinpointed in outbreak investigations ever suffer much more than bad publicity, no matter how rank the details in the inspection reports.”

Fresh Produce Shopping

Fresh produce

The reason it’s a good idea to put your produce in a bag with a twist tie when you are shopping is to prevent contamination onto other foods in your grocery cart or basket.

Salmonella, E.coli, and other food-borne illness have been linked to fruits and salads. Why? The dirt in which the food products are grown may be treated with animal manures containing germs or the crops may have been irrigated with sewage-polluted water. Plus, the crops themselves, such as apples, can fall where animals have been grazing. And finally, farm workers and food handlers who have enteric infections (a disease of the intestine), or whom don’t wash their hands after going to the toilet may contaminate products; or there may be poor sanitation in the fields or at the factory.

In the summertime, putting these types of foods in a hot car is tricky. Take a cooler or ice packs with you to the store and pack all the frozen, refrigerated or high-risk items straight into the cooler.

If something smells bad or if a seal is broken or a food is bulging out of a container, don’t taste it or eat it. If in doubt, throw it out.

Safe Kitchen

Limit cross-contamination of foods by washing fresh vegetables, salads and prepackaged salads before use. Don’t cut meat on a cutting board and then use the same board to cut vegetables.

Make sure that all food, and meat especially, are cooked to the correct temperature. Vigilance cannot be overrated.

And one last point, if you have any of symptoms of food poisoning, which often mimic the flu in earlier stages, make sure you tell the doctor what you’ve eaten.