On April 20, 2015, Blue Bell Creameries issued a voluntary recall for all of its products, including ice cream, frozen yogurt, sherbet, and frozen snacks, due to possible contamination with the bacterium Listeria monocytogenes. The company had found the bacterium in samples of Chocolate Chip Cookie Dough Ice Cream half gallons produced on March 17, 2015 and March 27, 2015. L. monocytogenes can cause a serious, sometimes fatal infection called listeriosis, especially in the young, the elderly, people with weakened immune systems, and pregnant women. In pregnant women, listeriosis can cause miscarriage, stillbirth, and other complications.

The U.S. Centers for Disease Control and Prevention (CDC) is urging consumers to throw away or return any unused used portions of Blue Bell products to the store. Through genetic testing of the bacteria (using a technique called whole genome sequencing), the CDC was able to identify strains of listeria associated with Blue Bell products and determine that the outbreak started as early as January 2010. As of April 21, 10 people had been hospitalized, and three people had died.

While Blue Bell Creameries may be the most high profile recall (after all, who doesn’t love ice cream?), it is just one in a series of listeriosis outbreaks in the United States, serving as a wake-up call to the threat of listeriosis. The CDC estimates that there are about 1600 cases of Listeriosis and 256 deaths per year due to the disease in the United States, making it the third leading cause of food-poisoning related deaths.

Just 10 days before the Blue Bell recall, hummus manufacturer Sabra had voluntarily pulled 30,000 cases of hummus off of shelves due to L. monocytogenes contamination. Earlier in 2015, Queseria Bendita issued a recall for its cheeses and sour cream; Radar Farms recalled its smoothie blend; and J.J. Funds issued a pet food recall.

These and other outbreaks have serious – sometimes devastating – effects. From December 2014 to February 2015, 35 people living in 12 states became ill after eating caramel apples contaminated with a different strain of Listeria monocytogenes. Eleven of those people were pregnant women, and one woman miscarried as a result of the illness. Seven people died.

Likewise, from August to October, 2014, five people became ill – including a newborn – after eating Oasis Brands cheese products that were contaminated with L. monocytogenes. One person died. Almost simultaneously – from August to November 2014 – five people were sickened and two died after eating contaminated sprouts produced by Wholesome Soy Products, Inc.

What is Listeriosis?

Listeriosis is an infection caused by the L. monocytogenes bacterium. Listeriosis occurs after someone eats food contaminated with L. monocytogenes. The bacterium is extremely hardy – it can survive extreme temperatures and lives in water, soil, poultry, cattle, and other animals. Generally, animals carry the bacterium in their intestines with no ill effects, so it’s difficult to determine whether an animal is infected without expensive testing. If an infected animal defecates, the bacterium can be introduced into the soil, contaminating any crops grown in the area.

Listeriosis occurs in two forms: a relatively mild disease called non-invasive gastrointestinal listeriosis, and a life-threatening infection called invasive listeriosis. Listeriosis usually developes within three days to three weeks of consuming a contaminated product, although the incubation period may be as long as two months.

Who is at Risk of Listeriosis?

Listeriosis can develop in anyone who eats food contaminated with L. monocytogenes. However, most healthy adults do not become ill after exposure. Some people are at much higher risk for developing listeriosis after exposure to L. monocytogenes, including pregnant women and their fetuses, newborns, adults 65 and older, and people with weakened immune systems.

Exposure to L. monocytogenes is common, but full-blown disease is rare even in high-risk populations. For instance, researchers who studied a 2011 outbreak related to contaminated cantaloupe found that 1 in 10,000 pregnant women who ate the cantaloupe became ill. For pregnant women and their fetuses, the disease is especially dangerous. Although pregnant women may not show any symptoms, data from the CDC show that from 2004 to 2009, one out of three (29%) pregnancies affected by listeriosis ended in either miscarriage or stillbirth.

Because invasive listeriosos is so dangerous when it does occur, it is important to prevent exposure.

What are the signs and symptoms of Listeriosis?

Early symptoms of Listeriosis often include diarrhea, nausea, and vomiting. Fever and body aches often follow. Other symptoms of Listeriosis depend on the affected person. In pregnant women, listeriosis often causes, in addition to gastrointestinal distress, fever, and achiness, vague symptoms such as tiredness. Infection can have dire consequences for both the pregnant woman and her fetus, including miscarriage, stillbirth, or premature delivery. Infection of the newborn is life threatening.

Other symptoms may include – in addition to fever and body aches – headache, stiff neck, confusion, convulsions, and loss of balance. Very young children, older adults, and people with weakened immune systems are especially susceptible to meningitis (inflammation of the meninges, the lining around the brain and spinal cord). They are also at high risk of the bacteria entering the bloodstream, causing septicemia (sometimes referred to as “bactermia” or “blood poisoning”).

Symptoms in otherwise healthy people may vary widely. They may experience gastrointestinal problems such as diarrhea, nausea, and vomiting, or they may have no symptoms at all.

What is the treatment for Listeriosis?

Treatment for Listeriosis depends largely on signs and symptoms. Generally, doctors will recommend the following courses of treatment if a person in the “high risk” category – i.e. a pregnant woman, a young child, a person 65 years or older, or someone with a weakened immune system – has consumed a food known to be contaminated with L. monocytogenes and is in the following state of health:

No symptoms: If someone has consumed a contaminated food but has developed no symptoms, most experts recommend a “watch and wait” approach. No testing or treatment is generally recommended, but people are advised to return if they develop any symptoms or within two months after eating the recalled product.
Mild symptoms: If a person is experiencing mild symptoms such as mild nausea, possibly vomiting, and diarrhea, but no fever or achiness, the physician and doctor should work together to determine a course of treatment. Some clinicians choose to treat people who are mildly ill as if they have a full-blown infection by prescribing antibiotics. Other doctors also perform a culture, often starting an antibiotic while waiting for culture results. If the culture shows infection with L. monocytogenes, a full antibiotic regimen is prescribed. Antibiotics generally include IV ampicillin and gentamicin. The doctor may choose not to prescribe gentamicin in pregnant women.
Symptoms including fever: All people who develop a fever greater than >100.6° F (>38.1° C) and other symptoms such as diarrhea, nausea, vomiting, and achiness after known exposure to L. monocytogenes should receive immediate screening and antibiotic treatment. Screening should include a blood culture. The doctor will choose other tests based on the person’s condition, such as a culture of the cerebrospinal fluid. Stool cultures are generally not performed, as they have not been tested as a reliable indicator of L. monocytogenes infection. If the culture shows the person is infected, a full antibiotic regimen is prescribed, lasting 14 to 21 days. Antibiotic treatment is discontinued when all symptoms have resolved and the blood culture is negative.
No symptoms now, but symptoms in the previous 4 weeks. Generally, doctors do not recommend any testing or treatment for someone who ate a contaminated food, experienced symptoms of listeriosis, but is no longer showing any signs or symptoms of the disease. However, if the person develops signs or symptoms again within two months of eating the recalled food, he should seek a physician’s care immediately. In a pregnant woman, the doctor may choose to monitor or test the fetus for infection.

How can you protect yourself and your family?

You can minimize your chances of developing listeriosis by adopting good food safety and kitchen hygiene habits and avoiding high-risk foods.

Adopt good food safety and kitchen hygiene habits:

Keep your refrigerator 40 degrees Fahrenheit (X Celsius) or below
Microwave wet sponges for one minute to kill bacteria. Do this before and after wiping down countertops, cutting boards, and knives.
Keep your kitchen clean
- Wash your hands carefully and thoroughly before and after preparing food
- Wash countertops, cutting boards, and knives after preparing uncooked foods
Carefully prepare all raw vegetables and fruit:
- Rinse raw produce under running tap water before eating, cutting, or cooking – even if it will be peeled.
- Scrub firm produce, such as melons and cucumbers, with a firm, clean produce brush. Sanitize the brush in between foods.
- Dry produce with a clean cloth or paper towel
Treat uncooked meats, fish, and poultry carefully
- Store them separately from vegetables and prepared foods
- Use a separate cutting board for meats, and wash it thoroughly between uses, adding a few drops of bleach to the final rinse water
- Cook meat thoroughly, to the temperature recommended by the USDA

Throw out any uneaten leftovers after 3 to 4 days

Avoid high-risk foods:

While L. monocytogenes can occur in almost any food, a few culprits are more common than others. People who are at high risk – especially pregnant women – should avoid the following foods altogether:

Raw milk and any cheese made from raw milk. Despite claims about superior health benefits of raw milk from proponents, raw milk is not nutritionally superior to pasteurized milk – and it can harbor microorganisms that can make you sick. In addition to L. monocytogenes, raw milk can harbor E. coli and Salmonella, two notorious players in the world of foodborne illnesses.
Soft cheeses made with unpasteurized milk. Avoid soft cheeses such as Brie, Camembert, blue-veined cheeses, and Mexican-style soft cheeses such as Queso Fresco, Panela, Asadero, and Queso Blanco if they are made with unpasteurized milk. These cheeses are generally considered safe if they are made with pasteurized milk.
Cold deli meats and hot dogs, including luncheon meats, cold cuts, fermented or dry sausages, or other meats such as bologna. If you enjoy eating these meats, heat them to at least 165 degrees Fahrenheit before consuming them.
Refrigerated pâté or meat spreads from a deli or meat counter or from the refrigerated section of a store. Meat spreads and pâtés that do not need refrigeration are considered safe.
Refrigerated smoked seafood, unless it is in a casserole that has been thoroughly cooked. Avoid fish, including salmon, trout, whitefish, cod, tuna, and mackerel, that is labeled “nova-stile,” “lox,” “kippered,” “smoked,” or “jerky.”
Sprouts: Yes, sprouts. That healthy-looking, vitamin-packed, fiber-rich, crunchy container of sprouts is probably teeming with bacteria (and not only L. monocytogenes, but that’s another story). Here’s the short version of why: Sprouts need warm, moist conditions to grow. So do bacteria.
Unpasteurized, fresh-squeezed juice: Juices that have not been pasteurized pose a potential threat, as well. Only drink pasteurized juice out of bottles that have been fully sealed.

Other types of fruits and vegetables can also harbor the bacteria but shouldn’t necessarily be avoided – just prepared with extra care. Melons, including cantaloupe, muskmelon, honeydew, and watermelon are notorious culprit. A 2011 listeria outbreak in cantaloupes led the CDC and FDA to issue specific safe handling precautions for all types of melons. Bacteria, including L. monocytogenes can be difficult to wash from the rough surface of the cantaloupe rind.

The CDC recommends the following safety precautions when handling melons:

Wash hands with warm water and soap for at least 20 seconds before and after handling any whole melon, such as cantaloupe, watermelon, or honeydew.
Scrub the surface of melons such as cantaloupes with a clean produce brush under running water and dry them with a clean cloth or paper towel before cutting. Sanitize the scrub brush after each use to avoid transferring bacteria between melons.
Consume cut melon or refrigerate promptly. Keep your cut melon refrigerated at 40 degrees F (32-34 degrees F is best) or less for no more than 7 days.
Discard cut melons left at room temperature for more than 4 hours

Additional Resources

Centers for Disease Control and Prevention. Listeria. http://www.cdc.gov/listeria/index.html

Food and Drug Administration. FDA Investigates Listeria monocytogenes in Ice Cream Products from Blue Bell Creameries. http://www.fda.gov/Food/RecallsOutbreaksEmergencies/Outbreaks/ucm438104.htm

FoodSafety.gov on Listeria: http://www.foodsafety.gov/poisoning/causes/bacteriaviruses/listeria/index.html