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Listeria Caramel Apples: What We Have Learned

Posted in Food Safety,Listeria,Outbreaks & Recalls on October 12, 2018

Halloween is getting closer, which means that it’s time for unfounded rumors on Facebook. That’s right: fall is barely here, it’s still basically summer, and yet someone on your newsfeed is already gearing up to share a story about Halloween candy that’s been poisoned. It’s a very old tradition to get worked up about a random poisoner harming your children through malfeasance, even though multiple examinations of police records and newspaper stories from the past 50+ years have found scant evidence that anyone has ever done this.

That doesn’t mean that Halloween treats are all safe, of course. Fans of caramel apples got an unexpected surprise in the fall of 2014: 35 people across 12 states fell ill with listeriosis that originated in the sweet seasonal treat. All but one were so sick that they had to be hospitalized. Eleven of the cases were pregnancy related (listeria can wreak havoc on a pregnant woman or a newborn), and the Centers for Disease Control recorded one fetal loss. Seven deaths were reported in all, of which at the time of this writing listeriosis was definite cause for at least three.

We know that caramel apples were behind the outbreak because of the due diligence of government investigators, who set to investigating victims in hopes of determining the source of the listeria bacteria. 90% of the victims they interviewed reported eating caramel apples before falling ill. And not just any kind of caramel apples: theirs were pre-packaged and commercially sold, albeit under the banner of several different caramel apple brands, indicating that they may have shared a point of origin at an apple supplier.

A break in the case came shortly after. Bidart Bros, an apple supplier in Bakersfield, California, submitted to a regular FDA inspection in December of 2014. Investigators took more than a hundred swabs of different surfaces and machinery while there. They took the swabs back to the lab to culture any microbes that had been picked up, and there made an unfortunate discovery: seven of the swabs that they’d taken had grown little petri-dish populations of listeria monocytogenes. Additionally, the investigators found relevant maintenance problems with the equipment used to package the apples; in various places, it was chipped, frayed, or otherwise weathered so that disinfection and cleaning of pathogens like listeria would prove difficult.

In light of this finding, Bidart Bros voluntarily recalled several lots of their Granny Smith and Gala apples. Subsequent genetic analysis of the listeria from Bidart Bros found that it was genetically indistinguishable from the outbreak strain that had laid more than thirty people low earlier in 2014. After Bidart Bros had put out their voluntary recall notice, three caramel apple producing operations that sourced from Bidart issued recalls of their product. Those recalls were followed by more findings from the FDA, who had supplemented their initial genetic analysis of the listeria with a more in-depth look through whole genome sequencing. That process confirmed their earlier findings; the listeria at the Bidart Bros facility was closely genetically related to the listeria taken from patients who had fallen ill during the outbreak.

In some ways, tracing the outbreak back to Bidart Bros raised as many questions as had been answered. Caramel apples aren’t normally thought of as likely carriers for listeria. Apples in general aren’t; they’re highly acidic, which isn’t the sort of environment that listeria usually thrives in. The bacteria is usually confined to the surface of the apple – without bruising or laceration to exploit, it can’t usually get past the skin of the apple to spread inside, and the skins are generally cleaned during the manufacturing process. The application of caramel poses another hurdle to listeria bacteria: before it’s applied to the apple, the caramel is heated to between 170 and 200 degrees Fahrenheit. Those temperatures should be above the range at which listeria can survive.

A follow up study in the Journal of Food Protection puzzled through how apples can be contaminated with listeria despite these significant hurdles. They found that the trick is in the application of the stick with which caramel apples are held while being eaten. The stick usually goes in at the stem end, one of the places on the outside of the apple where pathogens have a natural hollow in which to breed or survive disinfection. When it goes in, the pressure applied to the stick shoves it against the flesh of the apple, expressing a bit of sugary apple juice from the fruit. That juice makes for a nutrient-rich environment in which pathogens like listeria can thrive. The sort of stick matters too: listeria did significantly better on sticks made of paper or wood than they did on plastic.

What about the caramel, though? That all depends. Although the caramel is hot enough at the point of contact to eliminate any bacteria that it comes into contact with, there are other variables in the equation: how the apple is shaped, how the caramel is applied, and where the bacteria are located on the apple all need to be considered. Survival of the bacteria hinges on the these factors and the micro-environment that it finds itself in while the caramel is being applied. In many cases, pockets of listeria were able to survive the application of caramel by virtue of where they were and the relatively quick cooling of caramel on their part of the apple. To quote the authors of the paper, “the data indicate that manufacturers should not consider hot caramel dip a lethality step sufficient to reduce or eliminate the risk of L. monocytogenes contamination on caramel apples.”

Hopefully, this incident inspires caramel apple manufacturers to be more careful about listeria. You can be careful, too: wash your apples thoroughly before eating them or coating them in caramel, and opt for plastic sticks if you’re more worried about food safety than the environment. Don’t trust the application of the caramel will be hot enough to cleanse the apple or stick.

Also remember that you’re more likely to get listeria from your more mundane interactions with fruit. Exercise particular caution with surfaces, utensils, and fruit that’s been cut into slices: listeria bacteria can travel from the rind, the counter, cutting board, or knife to the flesh of the fruit after it’s been cut. Finally, don’t forget that it’s more likely you find pathogens than razor blades or pins and needles in your holiday treats. Whatever you’ve heard on the local news or from your gossipy neighbor about tainted candy is more likely a prank, rumor, or hoax than a real threat.

By: Sean McNulty, Contributing Writer (Non-Lawyer)