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Listeria in Lettuce; What You Can do to Protect Yourself

January 29, 2016

By: Melinda Hayman, PhD, Director of Microbiology, Jennifer McEntire, PhD, Vice President, Science Operations

The CDC estimates that over 48 million people suffer from foodborne illness annually but serious illness disproportionately impacts vulnerable populations such as the young, elderly and immune-compromised.

Generally people get sick from eating food that is contaminated from viruses or bacteria.  The results can be a fairly mild but unpleasant illness (such as vomiting and diarrhea), but tragically, these illnesses can also result in chronic illness or death- especially in sensitive populations.

One of the most deadly foodborne bacteria is Listeria monocytogenes (Lm), which causes the disease listeriosis.  Thankfully this disease is fairly rare, with about 800 cases diagnosed annually in the U.S.  This illness has traditionally associated with deli meats, hot dogs, smoked fish and soft cheeses.  If you have ever been pregnant and your doctor told you to avoid these foods, this is why.

Recently there have been a number of listeriosis outbreaks attributed with foods that don’t typically come to mind when we think of Lm.  In the past week there has been a well-publicized outbreak associated with bagged lettuce.  Bagged salads have previously been linked to other types of foodborne illness, but not listeriosis.  To date (January 28, 2016) 15 people have contracted listeriosis; the youngest patient a 3-year old child.  All of these people were hospitalized and one person has passed away.

This outbreak started in July 2015, and was detected by whole genome sequencing (WGS).  WGS is a tool used by public health agencies that can identify an organism and show the relatedness between patient and food isolates.  Even though highly related patient isolates had been collected in late 2015; it was not until a couple of weeks ago that the food was identified.

What can you do to protect yourself and your family from listeriosis?

  • Listeriosis affects mainly the elderly (those aged 70 +), people with weakened immune systems and pregnant women, and rarely affects healthy adults and children.
  • If you are pregnant, elderly or immunocompromised then you are at a higher risk for contracting foodborne disease.
  • People who fall into these categories should avoid eating foods that have historically been associated with Listeria, and especially soft cheeses made with raw milk.
  • It is OK to eat foods such as deli meats and hot dogs if they are cooked prior to consumption, since that will kill the bacteria.
  • In addition to the foods listed above avoid pre-cut fruit and pre-cut raw vegetables (such as bagged salads) and sprouts.
  • The FDA has further resources targeted at informing consumers, such as these food safety facts sheets for vulnerable people.

Food safety professionals, including the food industry, regulators and scientists, are all working on reducing the illnesses associated with Listeria and other foodborne pathogens.  GMA has been actively engaged on the issue for some time and is working with the food industry to reduce the prevalence of Lm.


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