Preventing Listeria Infection
Important food safety measures should be followed to prevent Listeria infection, especially among the elderly, pregnant women, and those who are immunocompromised.
Given its prevalence in the environment and the fact that the vast majority of Listeria infections are the result of consuming contaminated food or water, preventing illness and death is undoubtedly a food safety issue.
L. monocytogenes presents a particular concern with respect to food handling because it can grow at refrigerator temperatures (4°C to 10°C), temperatures commonly used to control pathogens in foods. Freezing also has little detrimental effect on the microbe. Although pasteurization is sufficient to kill Listeria, failure to reach the desired temperature in large packages can allow the organism to survive. Food can also be contaminated after processing by the introduction of unpasteurized material, as happens during the preparation of some cheeses. Listeria can also be spread by contact with contaminated hands, equipment, and counter tops.
The use of irradiation to reduce Listeria to safe levels in foods has many proponents. As noted by an eminent CDC researcher, Robert V. Tauxe:
Ready-to-eat meats, such as hot dogs, have already been subjected to a pathogen-killing step when the meat is cooked at the factory, so contamination is typically the result of in-plant contamination after that step. Improved sanitation in many plants has reduced the incidence of infection by half since 1986, but the risk persists, as illustrated by a large hot dog-associated outbreak that occurred in 1999. Additional heat treatment or irradiation of meat after it is packaged would eliminate Listeria that might be present at that point.
To further decrease the risk of Listeria on ready-to-eat foods, there are rules in USDA Food Safety and Inspection Service (FSIS) inspected facilities to address the risk of post-process Listeria contamination. As of 2014, the most current version of 9 CFR 430, also known as The Listeria Rule, states that processing facilities must control for the pathogen by using either post-packaging lethality treatment, as aforementioned by Dr. Tauxe, anti-microbial additives, or a process to render the product unable to sustain contamination by L. monocytogenes, environmental sanitation, or a combination of these. Processing plants also must implement an environmental testing plan.
The CDC provides a comprehensive list of recommendations and precautions to avoid becoming infected with Listeria, which are as follows:
- Keep your refrigerator at 41°F (5°C) or below to slow the growth of Listeria.
- Ready-to-eat foods, such as deli items and leftovers, should be stored no longer than seven days at or below 41°F
- Thoroughly cook raw food from animal sources, such as beef, pork, or poultry to a safe internal temperature. For a list of recommended temperatures for meat and poultry, visit the USDA Website.
- Avoid getting fluid from hot dog and lunch meat packages on other foods, utensils, and food preparation surfaces, and wash hands after handling hot dogs, luncheon meats, and deli meats.
- Rinse raw fruits and vegetables thoroughly under clean running tap water before eating.
- Keep uncooked meats, fish, and poultry separate from vegetables, and from cooked foods and ready-to-eat foods while shopping and in storage.
- Do not drink raw (unpasteurized) milk, and do not eat foods that have been made from or include unpasteurized milk.
- Eat cut melon within four hours or refrigerate it at or below 41°F for no more than seven days.
- Wash hands, knives, countertops, and cutting boards after handling and preparing uncooked foods.
- Consume perishable and ready-to-eat foods as soon as possible.
There are additional recommendations for persons at increased risk of infection, such as pregnant women and persons with weakened immune systems. In addition to the recommendations listed above, CDC advises the following:
- Do not eat hot dogs, luncheon meats, cold cuts, other deli meats (e.g., bologna), or fermented or dry sausages unless they are heated to an internal temperature of 165°F just before serving.
- Do not eat refrigerated pâté or meat spreads from a deli or meat counter or from the refrigerated section of a store. Foods that do not need refrigeration, like canned or shelf-stable pâté and meat spreads, are safer to eat. Refrigerate after opening.
- Do not eat soft cheese such as feta, queso blanco, queso fresco, brie, Camembert, blue-veined, or panela (queso panela) unless it is labeled as made with pasteurized milk. Make sure the label says, "MADE WITH PASTEURIZED MILK."
- Do not eat cold smoked seafood, unless it is contained in a cooked dish, such as a casserole, or unless it is a canned or shelf-stable product.
- Cold smoked seafood, such as salmon, trout, whitefish, cod, tuna, and mackerel, is most often labeled as "nova-style," "lox," "kippered," "smoked," or "jerky." These fish are typically found in the refrigerator section or sold at seafood and deli counters of grocery stores and delicatessens.
- Canned and shelf stable tuna, salmon, and other fish products are considered safe to eat.
- Do not eat raw or lightly cooked sprouts, regardless of type.
- Cook sprouts thoroughly before consuming.
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 41°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.
Additional preventive steps and precautions can be found on the websites of most state departments of health, and on CDC’s and FDA’s websites.