Listeria can cause serious and sometimes fatal infections called listeriosis in the young, elderly or those with a weakened immune system. Listeriosis can also cause pregnant women to have miscarriages or stillbirths, which seems like a particularly cruel risk for pregnant women craving a scoop or two.
But is there actually a growing listeria problem? Or are we merely getting better at detecting the bacterium in our food?
Experts say that more listeria-related recalls doesn’t mean incidents of contamination are on the rise. Instead, what’s more likely is that manufacturers are becoming more aware of new or surprising foods that can harbor listeria (it isn’t just hot dogs and cold cuts anymore!), and that they’re testing their facilities more often. In addition to ice cream, fruits and vegetables have also been recalled for listeria contamination in recent years.
“We’re looking into different food systems and our awareness of where [listeria] is is changing, which is actually good news in a way,” said Haley Oliver, an associate professor of food science at Purdue University. “The more we understand which foods are potential risk factors or potential reservoirs, the more likely we are to actually reduce listeriosis.”
If you’re worried about the safety of your food, here’s what you should know about the rash of listeria-linked recalls in foods ― and why ice cream is a particularly welcoming environment for the bacterium.
Pasteurization doesn’t necessarily prevent contamination
You might think that, given the mandatory pasteurization process to which ice cream makers adhere, bacterial contamination wouldn’t be a problem.
But Oliver said the process, which heats the food to kill any bad bugs, happens early in the ice cream production, often before the addition of flavors, colors and mix-ins, and definitely before it’s packaged into individual tubs. That means there’s a lot of opportunity between the heat treatment and the final packaging seal for bad bacteria to sneak its way in through your most beloved flavors and mix-ins.
For example, Blue Bell ice cream recalled their cookie dough and cookie two step flavors on Oct. 10, not because there was listeria in the the ice cream itself, but because cookie dough supplied by a separate company called Aspen Hills, Inc., may have been contaminated with the bacterium. The same goes for Blue Bunny’s hoppin’ holidoodle ice cream, because it also contained Aspen Hills’ cookie dough, as did recalled ice cream from Publix and Chocolate Shoppe Ice Cream.
Why listeria thrives in ice cream: cold temperatures and poorly-designed processing plants
Listeria is commonly found in water and soil, and thrives in cold temperatures. It can survive in refrigerators, and freezing listeria doesn’t kill it — it just puts the bacterium in a state of suspension.
Listeria can be introduced to mixing blades and freezers through water that drips from leaking pipes or hoods that collect condensation, for example. If a plant is poorly designed so that the equipment can’t be broken down and sanitized, or if workers can’t reach the equipment to clean it, then the factory can potentially harbor listeria.
For example, an October recall of certain Nestle cones happened because investigators found listeria on the surface of a production line.
“It’s all about making sure your lines are hygienically designed and that you have good manufacturing protocols in place,” says Samuel Alcaine, an assistant professor who specializes in dairy fermentation at Cornell University. “It is something everyone should be able to do if they’re paying attention.”
There are some ways to lower the risk of listeriosis
Because listeria can thrive in cold temperatures, one way to protect yourself against infections is to clean your fridge shelves and drawers regularly with warm, soapy water. Keep foods that are meant to be cold in the fridge or freezer, and throw out leftovers after three days, the U.S. Food and Drug Administration advises.
The only way to kill listeria is with heat, so when you’re microwaving or reheating refrigerated food, do it thoroughly until there are no more cold spots on the plate, said Oliver. Unfortunately, doing the same thing to ice cream would destroy it.
Alcaine also advised pregnant women to both discuss the risks of certain foods with their doctor and keep up to date on all the recent recall news, so that they get a sense of which kinds of foods to be more cautious about.
“Talk to your doctor about understanding your risks, and understanding if you have a weakened immune system,” says Alcaine. “Be aware which products have a higher incidence of listeria, and then be cautious about eating those.”
Dr. Laura Riley, vice chair of obstetrics at Massachusetts General Hospital and past president of the Society for Maternal-Fetal Medicine, is equivocal on whether pregnant women should avoid ice cream, pointing out that it certainly isn’t the healthiest source of calcium. On the other hand, she did admit that if she had to be pregnant all over again, she’d be “very sad” if someone told her to stop eating ice cream.
“You can make pregnant women crazy with, ‘You can’t have this, you can’t have that,’” Riley cautioned. “This makes for a really unpleasant nine months.”
Riley also pointed out that the benefits of fresh fruits and vegetables for a pregnant woman and her fetus are too great, and the risk of listeriosis too small, for women to avoid fresh produce altogether.
“We need to be really cautious about taking out whole food groups because of some [risk] that is a really tiny percentage,” she said.
No matter what they eat, Riley said, pregnant women need to keep basic food safety standards in mind: Wear gloves while gardening to guard against listeria and other harmful pathogens and thoroughly wash (and scrub, if necessary) fruits and vegetables before eating them.
If you’re especially at risk of a listeriosis infection, or if you’re pregnant, practice good food safety protocol, pay attention to the recall news and continue to eat a balanced diet. If you want to reduce your risk even further, eat cooked vegetables more than raw ones and talk to your doctor about any other preventive steps you can take to make a low risk even lower.