Listen Up About Listeria

July 30, 2024

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A Listeria monocytogenes (Listeria) outbreak in the United States tied to contaminated deli meat has killed two people and hospitalized an additional 28 from May to July 20, 2024. (1) The two deaths occurred in Illinois and New Jersey, with hospitalizations in Delaware, Georgia, Maryland, Massachusetts, Minnesota, Missouri, New York, North Carolina, Pennsylvania, and Virginia.

Meanwhile, in Canada, health authorities reported two people died from Listeria in July after consuming plant-based alternatives to dairy milk. The month before, Totally Cool recalled dozens of ice cream products due to potential Listeria contamination. (2)

Listeria has a mortality rate of 20% to 30%

Even with antibiotic treatment, Listeria has a mortality rate of 20% to 30%. (3) In the United States, an estimated 1,600 people contract Listeria annually, resulting in about 260 deaths. The hospitalization rate is 94%, meaning that of the approximately 1,600 people infected yearly, about 1,500 will end up hospitalized. (4)

What is Listeria?

Listeria is a foodborne bacterial infection that can be very serious for pregnant women, people 65 or older, and those with weakened immune systems. It can cause pregnant women to miscarry or deliver prematurely, and it can be life-threatening for newborns, who can be infected by their mothers.

The most common carriers of Listeria are improperly processed meats and unpasteurized milk products, although other causes include fruits and vegetables grown in contaminated soils, fertilizer, or feces.

Listeria bacteria can survive on surfaces for a long time, including one documented case of it continuing to contaminate a food processing plant for 10 years. (5) Listeria-contaminated food, in turn, contaminates the surfaces and equipment used to prepare and process the food. The bacteria form biofilms that attach to surfaces like stainless steel.

Symptoms of Listeria Illness

Listeria usually causes flu-like symptoms, such as headache, fever, muscle aches, chills, vomiting, diarrhea, and fatigue. However, if the infection spreads to the nervous system, symptoms can include a stiff neck, confusion, balance problems, and convulsions or seizures. (6)

infection can take 30 days or more to manifest

While symptoms often start a few days after contaminated food is ingested, in some cases, the infection can take 30 days or more to manifest and for symptoms to appear.

Source Identification

Scientists discovered the bacteria from samples of those infected by the recent deli-related Listeria outbreak were closely related genetically, suggesting that the people became ill from eating the same foods. This finding is thanks to a scientific process called whole genome sequencing (WGS), a kind of DNA fingerprinting of bacteria. (7)

All organisms—bacteria, plants, and animals—have a unique genetic code of nucleotide bases A, T, C, and G. WSG is a technology that allows scientists to identify the sequence of these bases, commonly known as DNA. (8)

WSG is widely used to identify foodborne illness outbreaks caused by bacteria, including Listeria. WSG is a significant help in tracking the outbreak’s source, which can help with product recalls and reduce the number of infections. It is also used to help explain why some bacteria make people sicker or more resistant to antibiotics than others.

Staying Safe

Most healthy people experience the symptoms above; older, pregnant, and immune-compromised individuals should take added precautions by avoiding foods most susceptible to the contamination, including:

Unpasteurized soft cheeses, milk, yogurt, and ice cream
Unheated deli sliced cold cuts and cheeses, hotdogs, and dry sausages
Refrigerated pâté, meat spreads, smoked fish
Cut melon that is two weeks old, unrefrigerated for two hours, or unrefrigerated for one hour at 90-degree or higher temperatures. (9)

Listeria is no fun. Knowing how to avoid it can help protect you and your loved ones.