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As concerns about listeria return to the headlines, here’s what to know about infection and food recalls

By Dr. Sarah D’Orazio
University of Kentucky

Listeria is in the news again – sometimes you’re warned against a particular brand of ice cream or bags of fresh produce. This time around, it’s deli meat. Public health officials will raise the alarm about an infection called listeriosis. But what is listeriosis, and how harmful is it?

Sliced deli meats have been a major source of the latest round of listeria infections (Photo form Creative Commons)

Listeriosis is caused by the foodborne bacterium Listeria monocytogenes. It is most dangerous when found in processed, ready-to-eat foods such as lunch meats, unpasteurized milk or cheeses and sliced or pre-washed fresh produce that are eaten without being heated to a temperature that can kill the bacteria. The recalls are often the result of FDA-mandated inspections that reveal the presence of a small number of the bacteria in the processed food product. Listeria monocytogenes are unlike most bacteria in that they can actually grow at cold temperatures, so the number of bacteria could rise to be a hazardous dose while the food is kept refrigerated in the store or in your home.

In otherwise healthy people, ingestion of Listeria-contaminated food will likely only cause a mild, self-limiting intestinal infection. But in people who are at higher risk, the infection can spread and cause life-threatening systemic infection.  Listeriosis is most likely to be severe in pregnant women and their newborns, adults aged 65 or older, and people with weakened immune systems. Although listeriosis is not common, it has a high mortality rate in high-risk individuals. An estimated 1,600 people get listeriosis each year in the US, and about 320 (20%) die.

High-risk foods include:

• Hot dogs and sliced deli meats
• Unpasteurized milk or soft cheeses
• Refrigerated pâtés or meat spreads
• Refrigerated smoked seafood
• Fresh produce that has been pre-washed, sliced or otherwise processed

Here are some tips to reduce your risks:

• Wash all fruit and vegetables before eating them
• Maintain your refrigerator at or below 40 degrees Fahrenheit
• Don’t let the juice from hot dogs or deli meats get on other foods 
• Heat deli meats and hot dogs until steaming before eating
• Eat refrigerated foods before their use-by date
• Eat ready-to-eat foods within four hours of taking them out of the fridge

When in doubt, throw it out. If you can’t remember when you opened it, or something about the smell and appearance seems off, throw it away.

Consuming dangerous foodborne bacteria will usually cause illness within two weeks of eating the contaminated food. If you think that you or a family member has a foodborne illness, contact your healthcare provider immediately.

Dr. Sarah D’Orazio, Ph.D., is associate professor in the Department of Microbiology, Immunology and Molecular Genetics at the University of Kentucky College of Medicine.

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