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October 13, 2015: Study Finds Cause of 2014 Caramel Apple Listeria Outbreak

Caramel Apple Listeria Outbreak News

Following the lethal caramel apple listeria outbreak of 2014, researchers have finally discovered the conditions under which this delicious Halloween treat became a hot bed for deadly bacterium. The exact source of the Listeria moncytogenes growth within the candy apples has been a mystery since neither caramel nor apples are especially vulnerable to bacterial growth; caramel does not contain enough waster and apples are too acidic to cultivate most pathogens.

The Caramel Apple Listeria Study

The study was published by mBio, an open access journal published by the American Society for Microbiology, and involved exposing Granny Smith apples to the strains of listeria that caused the 2014 outbreak. The apples were then prepared and stored under differing conditions. The researchers skewered half of the apples with wooden sticks, and stored half of each type of apples (skewered and not) at either room-temperature or refrigerated.

The result of this experiment revealed two main catalysts in the growth of Listeria moncytogenes: the presence of a stick in the apple, and the storage temperature of the apple. The study concludes that the wooden stick spreads juices from the apple upward to the surface of the apple, where the moisture collects under or in the caramel. This moisture creates an environment in which Listeria moncytogenes thrives. Storing this treat in room temperature further increases the chance of growing bacterium. A non-refrigerated caramel apple on a stick is an inviting incubator for Listeria moncytogenes.

To see the entire study, visit Growth of Listeria monocytogenes within a Caramel-Coated Apple Microenvironment.

About Listeria Food Poisoning

Listeria monocytogenes is a bacterium capable of causing a serious and life-threatening foodborne infection known as listeriosis. Listeriosis is caused by eating food contaminated with Listeria bacteria. Healthcare professionals may use the terms “Listeria monocytogenes” or “Listeria” when referring to the bacteria and “listeriosis” when referring to the infection.

The U.S. Centers for Disease Control and Prevention (CDC) estimate that there are 1,591 cases of foodborne listeriosis, resulting in 255 deaths, in the U.S. each year. Newborns, pregnant women, older adults, and those individuals with weakened immune systems are at greatest risk for developing listeriosis.

For more information, visit our Listeria Symptoms and Complications page.


If you or a loved one has been harmed in the 2014 Caramel Apple Listeria Outbreak, diagnosed with listeriosis, or have a question regarding your legal rights, you can request a free legal case evaluation by visiting our Listeria Food Poisoning Lawsuit Help page, or by calling the Weinberg Law Firm toll free at 877-934-6274. Our phones are answered 24/7.

The 2014 Caramel Apple Listeriosis Outbreak

By December 30, 2014, the U. S. Centers for Disease Control and Prevention (CDC) had announced that a total of 32 persons had been infected with the outbreak strains of Listeria monocytogenes in a fatal Listeria outbreak linked to eating prepackaged caramel apples. Ten cases were associated with a pregnancy (occurred in a pregnant woman or her newborn infant). One fetal loss was reported. Among those cases not associated with pregnancy, ages ranged from 7 to 92 years, with a median age of 66 years. Three cases of meningitis occurred in otherwise healthy children aged 5–15 years. Thirty-one of those sickened were hospitalized. Six deaths were reported. Listeriosis conclusively contributed to three of these deaths.

For more information on the 2014 outbreak, visit Caramel Apples Listeria Outbreak 2014.

Recommendations to Prevent Listeria Growth in Caramel Apples

This study concludes with some practical changes caramel apples manufacturers can use to be proactive against bacterial growth. These include:
• validated disinfection of the apple,
• addition of growth inhibitors to the caramel coating or apple wax,
• temperature-time controls.

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