How Does Listeria Spread in Deli Meat? A Look at the History and Ongoing Risks of Outbreaks

You may want to check the deli meat in your fridge … again. On Wednesday, August 29, the Centers for Disease Control and Prevention (CDC) issued a reminder to avoid recalled products due to  a growing listeria outbreak. Since the agency’s last update on August 8, nine people have died from the illness, with a total 57 people hospitalized across 18 states. The outbreak is now the largest in the country since 2011. But how does listeria spread and contaminate food? Here’s what to know about the history of this food borne illness and how to stay safe.

What to know about the current listeria outbreak

The CDC’s most recent update has urged consumers to avoid as well as check for remaining Boar's Head deli meat in their homes. The delicatessen supplier issued a recall of its ready-to-eat liverwurst and other deli meat products in late July over contamination concerns. These include ham, bologna, sausage and roasted bacon, though  the majority of reports sighted turkey or liverwurst.

Over a dozen new listeriosis cases have been reported since the recall. Additionally, the CDC stated that the number of illnesses is likely higher due to milder symptoms without testing.

According to the CDC, Boar’s Head products can have a long shelf-life, with some as late as October 2024. They advise checking packaging for product labels “EST. 12612" or "P-12612" inside the USDA mark of inspection.

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How listeria spreads into food

Listeria bacteria can spread to food in various ways, making it a particularly challenging pathogen to control. According to the U.S. Department of Agriculture (USDA), “Animals can carry Listeria monocytogenes (Lm) in their intestines without becoming sick. As a result, the bacteria may be spread to meat and dairy products.”

Normally, bacteria is killed by cooking or other heating methods like pasteurization. However, contamination occurs during the processing or packaging stages of food production. The USDA notes that “ready-to-eat food can become contaminated after processing, within the processing plant or along the route from the plant to your plate.” Deli meats, soft cheeses and other pre-packaged products like hot dogs are especially susceptible to listeriosis.

Once present, listeria can survive and even grow in refrigerated environments, which is unusual for most bacteria. According to the CDC, “It can remain on surfaces, like meat slicers, and foods, even at refrigerated temperatures. It can also take up to 10 weeks for some people to have symptoms of listeriosis.”

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The history of listeria

Listeria was first identified as a serious public health threat in 1924 by scientist E.G.D. Murray, who discovered the bacteria in laboratory rabbits. It was named Listeria monocytogenes in honor of the British surgeon Joseph Lister, who pioneered antiseptic surgery.

Though it remained relatively obscure for decades, the first known cases of listeria infection in humans were reported in the 1940s. It wasn’t until the 1980s, however, that listeria gained significant attention as a foodborne pathogen, following several large outbreaks linked to eating contaminated food products. Since then, listeria has been recognized as a persistent and dangerous threat to food safety.

Listeria outbreaks have periodically made headlines, with one of the most notable cases occurring in 2011. That year, a listeria outbreak linked to cantaloupes from a Colorado farm resulted in 33 deaths and 147 illnesses across 28 states. This outbreak marked one of the deadliest foodborne illness outbreaks in U.S. history and brought listeria into the public spotlight. Another outbreak in 2024 linked to queso fresco and cotija cheese made by Rizo-López Foods resulted in 26 cases and two deaths.

How to stay safe from listeria

To protect yourself and your loved ones from listeria, it's crucial to follow the CDC's safety guidelines. Pregnant women, older adults and those with weak immune systems are most at risk to test positive for the illness. Here’s what you should do to stay safe:

• Avoid all recalled deli products from Boar’s Head or throw them away.
• Those with a higher risk should avoid consuming sliced meats from deli counters unless heated to an internal temperature of 165°F or steamed hot before serving.
• Clean all household surfaces that may have come into contact with sliced deli meats.
• Call your healthcare provider immediately if you are experiencing symptoms of listeriosis and recently ate meats sliced at deli counters.
  • Symptoms of listeriosis include fever, muscle aches, headache, stiff neck, confusion, loss of balance and convulsions.
• Stay informed about any food recalls and promptly discard any recalled products to reduce the risk of listeria infection.

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This content is not a substitute for professional medical advice or diagnosis. Always consult your physician before pursuing any treatment plan .