Listeria Infections Increase with Higher Summer Temperatures

Listeriosis is a serious infection usually caused by eating food contaminated with the bacterium Listeria monocytogenes. According to the CDC, an estimated 1,600 people get listeriosis each year, and about 260 die. The infection is most likely to sicken pregnant women and their newborns, adults aged 65 or older, and people with weakened immune systems.

For a complete listing of outbreaks reported to CDC since 1998, please use the Foodborne Outbreak Online Database (FOOD Tool).

Higher summer temperatures make storing foods susceptible to foodborne illness. This summer, quite a few companies have pulled food products that have a higher chance of breeding listeria monocytogenes. The recalls have not been tied to actual outbreaks, but the companies have acted as a precaution.

Hot, summer weather brings family vacations, neighborhood cookouts—and increased risks for Listeria and other food borne pathogens in processing plants.

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What foods can be contaminated by Listeria?

Listeria monocytogenes has the potential to be present in all raw foods. Cooked foods can also be contaminated, usually as the result of post-process contamination. The pathogen has been isolated from a very wide range of processed foods including pâtés, milk, soft cheeses, ice cream, ready-to-eat cooked and fermented meats, smoked and lightly processed fish products and other seafood. L. monocytogenes is usually found only in low numbers (less than 10/g) in foods.

Signs and Symptoms of Listeria

Listeriosis can cause a variety of symptoms, depending on the person and the part of the body affected. Listeria can cause fever and diarrhea similar to other foodborne germs, but this type of Listeria infection is rarely diagnosed. Symptoms in people with invasive listeriosis, meaning the bacteria has spread beyond the gut, depend on whether the person is pregnant.

Listeria is most likely to sicken pregnant women and their newborns, adults aged 65 or older, and people with weakened immune systems. Other people can be infected with Listeria, but they rarely become seriously ill.

  • Pregnant women: Pregnant women typically experience only fever and other flu-like symptoms, such as fatigue and muscle aches. However, infections during pregnancy can lead to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.
  • People other than pregnant women: Symptoms can include headache, stiff neck, confusion, loss of balance, and convulsions in addition to fever and muscle aches.

People with invasive listeriosis usually report symptoms starting 1 to 4 weeks after eating food contaminated with Listeria; some people have reported symptoms starting as late as 70 days after exposure or as early as the same day of exposure.

Large Outbreaks of Listeria

In recent history, the worst outbreak took place in 2011 when a cantaloupe outbreak killed 33 and hospitalized 143. After public health investigators interviewed those infected and looked into where the bacteria came from, it was linked to Jensen Farms where the facility was overflowing with listeria monocytogenes. The brothers who run the farm plead guilty to sending contaminated foods across state lines and ended up paying fines, serving house arrest, and fulfilling community service.

The full list of recalled foods this summer have included:

  • Hummus
  • Dried fruit
  • Baked goods
  • Protein bars
  • Nuts
  • Soybean sprouts

Diagnosis and Treatment of Listeriosis

Listeriosis is usually diagnosed when a bacterial culture (a type of laboratory test) grows Listeria monocytogenes from a body tissue or fluid, such as blood, spinal fluid, or the placenta.

Listeriosis is treated with antibiotics.

Listeriosis Prevention

FDA recommends the following rules to  avoid Listeria infection

  • Thoroughly cook your food
  • Wash raw vegetables and fruits before consumption
  • Keep uncooked meats separate from other products which are cooked or ready for consumption
  • Avoid consumption of unpasteurized products
  • Wash utensils, knives and cutting boards with care

If a person is at high risk for the disease like a pregnant women or an immuno-compromised person, it is advised to

  • Not eat meat products without heating them to point where they are steaming hot
  • Avoid cross contamination of food products by using different and clean utensils while handling each product
  • Do not eat soft cheeses
  • Do not eat refrigerated meat products like meat spreads
  • Do not eat fish products that are refrigerated unless they are a part of a cooked food product like a casserole

FDA and USDA are working at the government level for the safety and quality assurance of food, to detect the presence of Listeria in different products. In case an infection as found the producers and the whole facility is inspected and in some cases the products are recalled.

National Center of Infectious Diseases (NCID)  investigates and helps local state public health departments regarding any Listeria outbreak reported. Early reporting, detection, and investigation of such outbreaks can help identify source of Listeria infection and help prevent the disease spread.

Recommendations to keep food safe

  • Be aware that Listeria monocytogenes can grow in foods in the refrigerator. Use an appliance thermometer, such as a refrigerator thermometer, to check the temperature inside your refrigerator. The refrigerator should be 40°F or lower and the freezer 0°F or lower.
  • Clean up all spills in your refrigerator right away–especially juices from hot dog and lunch meat packages, raw meat, and raw poultry.
  • Clean the inside walls and shelves of your refrigerator with hot water and liquid soap, then rinse.
  • Divide leftovers into shallow containers to promote rapid, even cooling. Cover with airtight lids or enclose in plastic wrap or aluminum foil. Use leftovers within 3 to 4 days.
  • Use precooked or ready-to-eat food as soon as you can. Do not store the product in the refrigerator beyond the use-by date; follow USDA refrigerator storage time guidelines:
    • Hot Dogs – store opened packages no longer than 1 week and unopened packages no longer than 2 weeks in the refrigerator.
    • Luncheon and Deli Meat – store factory-sealed, unopened packages no longer than 2 weeks. Store opened packages and meat sliced at a local deli no longer than 3 to 5 days in the refrigerator.