Listeriosis: A Severe Foodborne Disease

Every year, approximately 1,600 people in the United States contract a foodborne illness that, while rare, carries one of the highest mortality rates among all food poisoning cases. Listeriosis, caused by the bacterium Listeria monocytogenes, is the third leading cause of death from foodborne illness, claiming about 172 lives annually. Unlike most foodborne bacteria, this dangerous pathogen has a unique ability to thrive in cold environments, making it a persistent threat in our refrigerators and ready-to-eat foods.

Understanding Listeria monocytogenes 🔗

Listeria monocytogenes is a rod-shaped, gram-positive bacterium found naturally in soil, water, and decaying vegetation. What makes this bacterium particularly dangerous is its remarkable ability to survive and multiply at refrigerator temperatures, even as low as 31 degrees Fahrenheit. While most bacteria slow down or become dormant in cold conditions, Listeria continues to grow, making refrigerated foods a potential reservoir for infection.

The bacterium can be isolated through standard bacterial culture of normally sterile body sites. Among the twelve recognized serotypes of Listeria monocytogenes, three strains account for 95% of human illness, with serotype 4b being most commonly associated with outbreak situations.

Who faces the greatest risk? 🔗

Listeriosis doesn’t affect everyone equally. Certain groups face significantly higher risks of developing severe complications from this infection.

Pregnant women and their babies 🔗

Pregnant women are approximately 10 times more likely than the general population to contract listeriosis, with Hispanic pregnant women facing an even higher risk at 24 times greater likelihood. During pregnancy, changes in the immune system make women more susceptible to infection. While pregnant women may experience only mild flu-like symptoms or no symptoms at all, the consequences for their babies can be devastating.

Infection during pregnancy can result in miscarriage, stillbirth, premature delivery, or serious infection in the newborn. Nearly 25% of pregnancy-associated cases result in fetal loss or newborn death. Babies born with listeriosis may develop severe complications including meningitis, sepsis, or granulomatosis infantiseptica, a severe disorder affecting internal organs and skin.

Older adults and immunocompromised individuals 🔗

Adults over 65 years old face elevated risk because their immune systems become less effective at recognizing and eliminating harmful bacteria. People with weakened immune systems due to conditions such as HIV/AIDS, cancer, diabetes, or kidney disease are also at increased risk. Additionally, those receiving chemotherapy, high-dose steroids, or immunosuppressive medications face higher vulnerability to severe listeriosis.

Recognizing the symptoms 🔗

Listeriosis presents differently depending on whether the infection remains in the digestive system or spreads to other parts of the body.

Intestinal listeriosis 🔗

The less severe form causes gastrointestinal symptoms including fever, muscle aches, nausea, vomiting, and diarrhea. These symptoms typically appear within 24 hours of consuming contaminated food and usually resolve within one to three days. Because Listeria cannot be detected by routine stool culture, this milder form is rarely diagnosed outside outbreak situations.

Invasive listeriosis 🔗

The more serious form occurs when bacteria spread beyond the intestines into the bloodstream or nervous system. Symptoms of invasive listeriosis typically appear within two weeks of eating contaminated food but can take up to two months to develop. This form causes fever, severe muscle aches, headache, stiff neck, confusion, loss of balance, and seizures.

Invasive listeriosis is extremely serious. Nearly everyone with listeriosis is hospitalized, and the case-fatality rate reaches approximately 20%. In non-pregnant individuals, almost one in six people with invasive listeriosis die from the infection.

How listeria spreads through food 🔗

Listeriosis is primarily acquired through consuming contaminated food. The bacteria can contaminate food at any point during harvesting, processing, preparation, or storage. Past outbreaks in the United States have been linked to a wide variety of foods.

High-risk foods 🔗

Ready-to-eat refrigerated foods pose the greatest risk because they’re stored at temperatures where Listeria can multiply and are typically consumed without reheating. Particularly high-risk items include soft cheeses (especially those made with unpasteurized milk), deli meats, hot dogs, refrigerated pâtés, and smoked seafood. Mexican-style cheeses like queso fresco, queso blanco, and requesón have been repeatedly linked to outbreaks.

Raw or unpasteurized dairy products and foods made with unpasteurized milk can harbor Listeria. Raw vegetables contaminated from soil or manure, raw or undercooked sprouts, cut melons, and certain processed foods that become contaminated after manufacturing also present risks.

Cross-contamination concerns 🔗

Listeria can spread from contaminated foods to other items through shared cutting boards, utensils, or refrigerator surfaces. The bacterium can form biofilms on surfaces, creating an invisible slime layer that makes it particularly difficult to eliminate through normal cleaning.

Prevention strategies that work 🔗

Preventing listeriosis requires a multi-faceted approach combining proper food selection, storage, and handling practices.

Temperature control 🔗

Maintaining proper refrigerator temperatures is critical. Keep your refrigerator at 40°F (4°C) or below and your freezer at 0°F (-18°C). Use refrigerator thermometers to verify temperatures, as these cold conditions slow Listeria growth, though they don’t stop it entirely.

Food handling practices 🔗

Wash hands thoroughly with warm, soapy water for at least 20 seconds before and after handling food. Scrub raw vegetables with a brush under running water. Clean and sanitize cutting boards, countertops, and utensils after preparing food, especially after contact with raw meat or unwashed produce.

Use ready-to-eat foods as soon as possible after purchase. The longer refrigerated foods sit, even at proper temperatures, the more opportunity Listeria has to multiply. Clean refrigerator spills immediately and regularly sanitize interior surfaces to prevent bacterial buildup.

Smart food choices for high-risk individuals 🔗

Pregnant women, older adults, and people with weakened immune systems should avoid certain foods entirely. Don’t consume soft cheeses unless made from pasteurized milk and avoid all Mexican-style cheeses. Stay away from refrigerated pâtés, meat spreads, and smoked seafood unless they’re incorporated into cooked dishes.

Hot dogs and deli meats should be reheated until steaming hot (165°F internal temperature) before consumption. Avoid raw or lightly cooked sprouts of any kind. Cut melons should be eaten immediately or refrigerated and used within seven days. Never consume unpasteurized milk or products made from raw milk.

Responding to food recalls 🔗

If you’ve purchased food that’s been recalled due to Listeria contamination, don’t open or consume the product. Return it to the store for a refund or dispose of it in a sealed bag. Clean and sanitize any refrigerator surfaces that may have contacted the recalled product.

When to seek medical attention 🔗

If you’ve eaten recalled food or foods that may be contaminated and develop fever, muscle aches, nausea, or diarrhea, contact your healthcare provider immediately. This is especially critical for pregnant women, older adults, and those with weakened immune systems. Get emergency care if you experience high fever, severe headache, stiff neck, confusion, or sensitivity to light, as these may indicate bacterial meningitis.

Diagnosis requires laboratory culture from blood, cerebrospinal fluid, or other normally sterile body sites. Treatment typically involves intravenous antibiotics, with the standard regimen including ampicillin and gentamicin for 14 to 21 days.

What do you think? How confident are you in your current refrigerator temperature and food storage practices? Are there any high-risk foods in your refrigerator right now that might pose a danger to vulnerable family members or guests?

References

1. https://www.cdc.gov/listeria/hcp/clinical-overview/index.html
2. https://www.fda.gov/food/foodborne-pathogens/listeria-listeriosis
3. https://www.cdc.gov/listeria/risk-factors/index.html
4. https://www.cdc.gov/listeria/signs-symptoms/index.html
5. https://www.mayoclinic.org/diseases-conditions/listeria-infection/symptoms-causes/syc-20355269
6. https://www.fda.gov/food/buy-store-serve-safe-food/what-you-need-know-about-preventing-listeria-infections