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Prevent food poisoning from listeria bacteria

Ice cream isn't the only food where these deadly bacteria lurk

Published: June 05, 2015 06:00 AM

Ice cream lovers were shocked this spring when Blue Bell Creameries halted sales after an investigation by federal and state health officials revealed that its products were the cause of a deadly outbreak of food poisoning caused by listeria bacteria. But perhaps the most shocking thing is that Blue Bell products weren’t the only foods where listeria was a concern this year. Although no illnesses were connected to them, a wave of listeria-related recalls involving hummus, apple slices, frozen ravioli, and more occurred before and after the Blue Bell outbreak.

Not everyone who eats listeria-contaminated food gets sick, but when listeriosis (the name for the infection caused by listeria bacteria) hits, it hits hard. The Q&A below will tell you what you need to know about this potentially lethal form of bacteria, and what you can do to protect yourself and prevent food poisoning.

Q. What is listeria and how does it get into food?

A. Listeria monocytogenes is a bacterium found in soil, water, and decaying vegetation. Animals may carry it without appearing ill, and when those animals are processed for food, the resulting meat or dairy products can become contaminated.

Cross contamination from equipment or workers and poor hygiene are potential routes for listeria transmission. While federal health officials haven’t determined exactly how listeria wound up in Blue Bell products, the Food and Drug Administration (FDA) recently released reports from inspections it conducted from mid-March to early May at the company’s production facilities.

Inspectors observed several problems, including inadequate cleaning and sanitizing procedures for equipment and food contact surfaces at the Brenham, Texas, plant, where condensate from equipment overhead was seen dripping directly into containers of ice cream.

They also noted employees’ failure to thoroughly wash their hands at plants in Oklahoma and Alabama, where they also observed an employee’s apparently soiled shirt come into direct contact with the interior of a container that was being filled with ingredients for a batch of Bride’s Cake ice cream.

As with salmonella and E. coli, pasteurization and cooking foods to the proper temperature kills listeria, but freezing doesn’t. So if food has been tainted with listeria (or another bacteria) before being frozen, the bacteria will survive, though they won’t increase in number. Once that food is defrosted, though, it’s subject to bacterial growth.

But listeria is different from other bacteria in one important way: it can continue to grow at refrigerator temperatures and can multiply rapidly, spreading from one food to another. Listeria also can live for years on equipment in places food is prepared, including food processing plants, grocery stores, and delis.

Deli meat, soft cheeses, and hot dogs are high-risk foods for listeria.

Q. What foods are most often contaminated with listeria?

A. Ready-to-eat refrigerated foods, smoked seafood, pates, and meat spreads are a few of the high-risk foods. Deli meats and hot dogs can also be risky, unless they are cooked to an internal temperature of 165°F. Blue-veined and other soft cheeses including feta, brie and Camembert, queso fresco, queso blanco, and Panela are potential sources, too. The risk is greatest if these cheeses are made with unpasteurized milk, but according to the Centers for Disease Control and Prevention (CDC), some soft cheeses made from pasteurized milk also have caused listeria infections, most likely due to contamination during the cheese-making process.

Fresh produce also has been the source of listeria outbreaks. For example, raw bean sprouts were resposible for a 2014 listeria outbreak that killed two and sickened three people. (Sprouts require warm and humid growing conditions, which also are ideal for listeria growth, and rinsing sprouts doesn’t remove the bacteria.) In 2011, listeria-tainted whole cantaloupes from a single Colorado farm caused the deadliest U.S. foodborne disease outbreak in nearly 90 years, sickening 147 people in 28 states and killing 33. A federal investigation found unsanitary conditions at the farm’s processing facility, which was likely the reason the fruit was contaminated.

Pregnant women are 10 times more likely than other people to be infected.

Q. What are the odds of being infected with listeria, and how serious are the health risks?

A. Listeria is responsible for about 1,600 cases of foodborne illness a year. That’s a lot less than other types of bacteria—for instance, salmonella sickens about 1 million people, and norovirus affects about 5 million. Yet listeria is the third-leading cause of death from foodborne illness, according to the CDC. The majority of people who get sick from listeria end up being hospitalized, and the bug kills one out of five people it infects. The Blue Bell outbreak, for example, caused 10 illnesses, three of which were fatal.

Some groups of people should avoid high-risk foods because they are more likely to suffer from listeriosis and become severely ill. This includes people age 65 or older, who represent nearly 60 percent of cases. Also at higher risk are people of any age with weakened immune systems (including those undergoing chemotherapy or radiation) or conditions such as diabetes, alcoholism, and liver or kidney disease. In these groups, listeria often causes life-threatening bloodstream infections or meningitis.

Pregnant women are about 10 times more likely than the general population to be infected. Though the women themselves may experience only flu-like symptoms, listeria infections during pregnancy can cause miscarriages, stillbirths or lethal illnesses in newborns.

Hispanic pregnant women are about twice as likely as other pregnant women to get listeriosis. The CDC says this is probably because soft cheeses like queso fresco are a big part of their diets. Queso fresco caused an outbreak of listeriosis in California in 1985 that sickened 142 people, causing 20 miscarriages as well as killing 10 newborns and 18 adults. Most of the victims were pregnant Latinas or their infants.

People who aren’t in any of these high-risk groups usually experience only mild gastrointestinal symptoms, or none at all, after eating listeria-contaminated foods, but some do suffer from the bug’s more severe health effects. For instance, among the 34 hospitalized victims of a 2014 outbreak linked to pre-packaged caramel apples sold at supermarkets in several states were three otherwise healthy children between the ages of five and 15 who developed meningitis.

Consult our food safety and sustainbility guide for more information on protecting yourself from foodborne illness and the results of our tests on pork, shrimp, chicken, and turkey

Q. What listeria symptoms would I have if I got food poisoning from eating contaminated food?

A. People infected with listeria bacteria typically develop a fever along with muscle aches, diarrhea or other gastrointestinal symptoms, and headache. If the infection spreads to the nervous system, they may also experience additional symptoms such as a stiff neck, confusion, loss of balance, and convulsions.

Symptoms can appear within a few days of eating contaminated food. But they sometimes take up to two months to develop, which can make it difficult to identify the source of the infection. Doctors use blood or spinal fluid tests to diagnose listeriosis, and they treat it with antibiotics, often given intravenously.

Possible contamination of organic spinach triggered many product recalls this spring.

Q. What other types of food have been recalled recently due to contamination with listeria bacteria?

A. A variety of foods were recalled this year because testing showed that listeria could be present, even though no illnesses had been linked to these products at the time they were recalled—nor has the CDC reported anyone being sickened by them to date. They include: Greystone Foods’ Today Harvest Field Peas with Snaps, Silver Queen Corn, and Broccoli Florets; Goodseed and Henry’s Farm branded sprouts; Hyvee Pasta salad; Jamba At-Home Smoothie Kits; Jeni’s Splendid frozen desserts; Rising Moon Organics Frozen Ravioli; Sabra Classic Hummus; Subway and Sun Rich packaged apple slices.

Listeria contamination of a food used as an ingredient in other products can trigger multiple recalls. In March of this year, Coastal Green Vegetable Co.—a California supplier of organic spinach—announced a recall due to possible listeria contamination. A cascade of related recalls of frozen organic spinach quickly followed: Cadia Organic Cut Spinach, Wild Harvest Organic Cut Leaf Spinach and house brands sold by Meijer, and Wegmans. There also were recalls of other frozen products, such as La Terra Fina Spinach Artichoke & Parmesan Dip & Spread, and a variety of frozen meals from Amy’s Kitchen, including Amy’s Vegetable Lasagna and Amy’s Spinach Pizza. The companies said they had been informed by their organic spinach suppliers that they had received the potentially contaminated product, though they did not name the supplier. No illnesses were reported to date in relation to any of these recalls.

Ice cream has been the cause of listeria outbreaks.

Q. When companies recall listeria-contaminated foods, what do they do to make sure future products are safe?

A. Identifying the source of the bacteria and eliminating it is essential and can require steps ranging from setting up new sanitizing systems in production facilities to establishing new listeria testing requirements.

For example, Snoqualmie Gourmet Ice Cream announced in late December 2014 that it was recalling all of its products produced during that year because they had been linked to two cases of listerosis. The company then shut down its plant for a month to fully sanitize it. It also implemented new safety programs that required bacterial testing results from all of its suppliers, as well as third-party testing of its production facility and of all batches of ice cream prior to shipping, which was able to resume in late January.

When Blue Bell recalled all of its ice cream products in late April, it also halted production at its four plants to carry out an intensive cleaning program, which included major repairs and sanitizing equipment. But in a May 15 press release announcing layoffs at the company, Blue Bell said that the process of cleaning and improving its plants will take longer than anticipated. It also said it had no timeline for when it would begin producing ice cream again, and that when production does resume, it will be limited and phased in over time.

The ideal temperature for your fridge is 37° F.

Q. How can I make sure the food I eat is safe?

A. While it’s largely up to food producers and retailers to make sure the foods you’re buying aren’t contaminated with listeria, taking the steps below will help cut your risks of infection:

• Rinse raw fruits and vegetables thoroughly under running water—using a clean vegetable brush scrub on those with thicker skins—before cutting or eating. That even applies to foods with inedible peels like cantaloupe, to avoid spreading bacteria from the outside of the fruit to the flesh when you peel or cut it.

• Keep your fridge below 40° F (our experts recommend 37° F) and your freezer no higher than 0° F. Use a refrigerator thermometer to check those temperatures regularly. Even small increases in temperature cause any listeria bacteria present to multiply much more quickly, according to Ben Chapman, associate professor and food safety specialist at North Carolina State University. For example, 100 listeria cells (the term used for measuring the amount of bacteria present) in a food can grow into 1,000 cells in about eight days in a refrigerator set at 41° F. At 45° F, it would only take four days for 100 cells to become 1,000 cells.

• Limit storage time for refrigerated foods, especially opened ready-to-eat foods like deli salads and cut produce. Eat deli-sliced meats, or packaged-luncheon meats that have been opened, within three to five days. Hot dogs, once their packaging is opened, should be used within a week.

• Store leftovers no longer than 3 to 4 days in covered containers that are shallow to promote rapid, even cooling. Reheat them to 165° F and bring soups or sauces to a boil before eating.

• Wash your hands before and after handling food. Clean up all food spills in the fridge immediately and thoroughly clean your fridge regularly to avoid spreading any of the bacteria from one food to another.

Finally, even though the odds of getting listeriosis are low for most people, the health risks it poses are so serious that it’s worth keeping tabs on the latest listeria-related recalls on the Food and Drug Administration’s website. You can also sign up on the site to get safety alerts when recalls are announced—an especially good idea for anyone in high-risk groups.  

—Andrea Rock

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