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What is listeria? Facts you need to know

What you need to know about the food-borne bacteria that can make you sick.
Image: Listeria
Listeria itself is not a disease; it's a bacteria: listeria monocytogenes.BSIP / UIG via Getty Images

Every few months — sometimes even weeks — it seems there's another one: a wide-ranging product recall based on concerns of listeria contamination. This week, Panera Bread announced it would recall cream cheese products sold in its U.S. cafes over possible listeria contamination. But what exactly is listeria? How does it breed and why are listeria outbreaks so deadly?

After talking with a handful of experts, I've learned that this is one tricky food-borne pathogen. Which brings us to lesson number one, listeria itself is not a disease; it's a bacteria: listeria monocytogenes. “It's important to understand that listeria itself is not a medical disease — but can cause a disease process," says Dr. Runjhun Misra, DO, an internal medicine specialist in Oakland, CA. "When it leads to infection, that is called listeriosis."And you can get it when you eat something that has been contaminated with the bacteria.

Here are five things you need to know about listeria outbreaks.

1. Listeria Loves Certain Foods

And listeria (the bacteria, that is) is incredibly unique, or, in the words of Dr. Meghan May, associate professor of biomedical sciences at University of New England College of Osteopathic Medicine, "it is very cool, with a fascinating cell biology to it." Listeria bacteria behaves similarly to mold, preferring moist conditions, and can be found in soil, water and some animals.

“Certain foods that are more likely to contain listeria include unpasteurized milk and cheeses made from unpasteurized milk, melons, raw sprouts, hot dogs, pâtés, lunch meats, cold cuts, and refrigerated smoked seafood,” Karen Wong, medical officer with the Centers for Disease Control' s (CDC) Division of Foodborne, Waterborne, and Environmental Diseases told NBC News BETTER.

It’s odd that listeria can affect such a wide array of food types. Usually food-borne pathogens, like salmonella, which favors raw foods, are more particular, and easier to sniff out as potentially suspect. What about listeria makes it able to breed in both smoked meats and unpasteurized milk? It all comes down to temperature and environment.

About 30 percent of infected patients don't show any symptoms.

2. It's Okay In The Fridge, But Listeria Hates The Oven

"Listeria can grow at refrigeration temperature,” says May. “It can do that because it's used to living outside and not particularly bothered by [that level of cold].”

Though listeria can grow in the fridge, May notes that it does grow more slowly in the cold, which is why it’s critical to make sure your refrigerator is set at “under 40 degrees Fahrenheit,” says Dr. Misra, adding that when you do your grocery shopping, make sure no refrigerated items are out for longer than two hours.

One condition that listeria can’t endure is extreme heat. If you really want to be sure that bacteria is dead and gone, expose it to heat of “above 165 degrees Fahrenheit,” says Misra.

3. Listeria Can Be Deadly, But For Many It’s Not Harmful

If you are more or less in good health, young, and not pregnant, you may come into contact with listeria and not even know it.

“About 30 percent of infected patients don't show any symptoms,” says May. “The next biggest group [of those infected] have flu-like illnesses.”

If you fall among the latter, you’ll probably just be miserable for a few days as you would with any stomach bug, but your body should be able to clear it up on its own and you might not require medical attention. But really, it’s your body, your call, and if you’re violently ill, you should go to the doctor just to be on the safe side. Also, if you do have listeriosis, you’ll want the hospital to know so they can report it and be on the lookout for other cases.

Wong of the CDC notes that around 260 people die from listeriosis every year. Those who have the highest risk of fatal infection are older people (older than 50, Dr. May points out), people with HIV, cancer, diabetes, kidney disease, liver disease on immunosuppressant drugs or living with other immune problems, as well as newborns and pregnant women.

Dr. Misra explains that this high-risk group of people can come down with invasive listeriosos, “meaning the bacteria spreads beyond the gut. You may have a headache, stiff neck, confusion, loss of balance and seizures in addition to fever and muscle aches.” If you present any of these symptoms, it’s imperative to get to the doctor or ER right away. You will likely be admitted to the hospital and administered antibiotics through an IV.

Pregnant women really need to be especially vigilant because, as Dr. May explains, they may fall in that 30 percent that have no idea they're infected — or they’ll just feel like it’s a particularly bad case of morning sickness. They may pull through fine, but they can unknowingly pass the infection on to their unborn child, which can be terribly tragic, leading to miscarriage or stillborn birth as well as health complications once the child is born.

“We worry about meningitis [in newborns] and also, when they're taking their first breaths, they may contaminate their respiratory tract with listeria if the mother is infected,” says May. “It’s a very high-risk problem, but fortunately it doesn’t happen often.”

In fact, May and the other doctors interviewed here note, it is for this very listeria-related concern that pregnant women are told to avoid high-risk foods such as raw cheese and deli meat.

4. Listeriosis Symptoms Can Take Months To Manifest, and Spur A Wide Investigation

Listeriosis can be detected in blood or stool cultures, but it’s challenging to trace the source because the incubation period can be so long.

“The symptoms can take as much as 60 to 70 days to manifest,” says Dr Obianuju Helen Okoye, a public health physician and healthcare consultant in St Louis, MO. “The average incubation time is about three weeks.”

Once a patient is diagnosed with listeriosis, an intensive investigation begins, spearheaded by the department of public health.

While investigations of outbreaks can lead to recalls, there doesn’t need to be a case of listeriosis for a massive product recall to take place.

“They'll try to figure out the source to try and stop any possible outbreaks,” explains Dr. Okoye. “So they’re going to ask a lot of questions about what the patient has eaten in the past month and where. Then they’ll see if other people are reporting listeriosis and if they’ve had similar foods or been to similar places. It can be a long drawn out process.”

While investigations of outbreaks can lead to recalls, there doesn’t need to be a case of listeriosis for a massive product recall to take place. In fact, most of the time product recalls are totally unrelated to outbreaks and carried out in adherence to the law of “better safe than sorry.” Also, nobody wants to get tied up in a lawsuit.

Factories would rather issue a recall that then be in trouble,” says Okoye. “They have protocols they go through and they may realize that a certain protocol was violated, or that there was some other issue and so they can't take that risk.”

5. How to Keep Listeria Out Of Your Home

Doctors stress that there’s no way to be 100 percent certain that you’ve eliminated listeria from your kitchen. But there are ways to reduce the risk. Avoiding unpasteurized products is number one, second to which are some common sense tips such as washing fruits and vegetables very thoroughly through running tap water, not allowing raw meat touch other foods, ensuring that cutting boards and cooking utensils are extremely clean (and that the knife you’d use to chop the raw turkey is not also used to chop the fresh celery). And of course, wash your hands like crazy.

If you happen to have a product on hand that has been recalled, Wong advises that you put it “in a closed plastic bag placed in a sealed trash can; this will prevent people and animals from eating it,” and to “wash the refrigerator or freezer drawer and other areas where the recalled product was stored using hot water and soap.”

To find out what's been recalled in your area, see the FDA's list of recalled products.

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