This bacteria can live in almost any food—and infections are deadly in 1 in 5 cases. Here’s how to stay safe.
“Listeria is an infection-causing bacteria that contaminates food,” says Donald Schaffner, Ph.D., a food scientist and distinguished professor at Rutgers University. “It can cause a deadly illness called listeriosis.”
While months will pass without a peep in the news about listeriosis, an outbreak will light up your news feed faster than a Donald Trump tweet. That’s because listeriosis is deadly in 1 out of 5 cases. Also, Listeria is one of three germs that account for 91 percent of all “multistate” food-borne illness outbreaks, according to a report from the non-profit Robert Wood Johnson Foundation. (The other two are salmonella and E. coli.)
About 1,600 people contract listeriosis each year, per the CDC. But here’s the crazy thing: “Listeria is something you and I probably ingest all the time,” Schaffner says.
Huh? Keep reading.
Listeria Are Everywhere
From farms to food processing plants, Listeria “is widespread in the environment,” Schaffner explains. It's found in raw meat and produce, but refrigerated "ready to eat" foods are also sources.
So why aren’t we all getting sick from it?
“If you’re healthy, you usually have to ingest relatively high concentrations of Listeria to get sick—like hundreds of thousands or millions of organisms,” he says.
A report from the FDA found up to 10 percent of American adults may be carrying around Listeria in their systems right now. But when you hear about an “outbreak” on the news, or an FDA warning about contaminated food, those are referring to instances when improper food safety conditions allowed Listeria to proliferate in huge numbers.
Even If You’re Infected, You May Hardly Notice It
For healthy adults, listeriosis is often no big deal.
“You might have mild stomach upset for a day or two, but you could also experience no symptoms whatsoever,” Schaffner says.
Headache, muscle aches, fever, chills, and a stiff neck are some of the milder symptoms a healthy person might experience from listeriosis, the CDC says. Those symptoms usually last no more than 4 days, and could also involve a run to the bathroom every hour or two.
The big risks, Schaffner explains, are for the elderly, pregnant women, and people who have compromised immune systems—like those on cancer treatment drugs. While pregnant women may only notice flu-like symptoms, listeriosis can cause premature labor or miscarriage, or even stillbirth, the CDC says.
For older and sick people, a Listeria infection can spread to the blood, and from there cause organ failure or a deadly inflammation of the brain and spinal cord, Schaffner says.
But Healthy Men Aren’t Totally Safe
While you’re more likely to suffer a serious infection if you’re in one of those at-risk groups, listeriosis can still strike down healthy dudes, says Doug Powell, Ph.D., a former professor of food safety at Kansas State University and author of Barfblog.
“We all have genetic variabilities in terms of our risk for disease,” Powell says, “and we’re not smart enough yet to know who we might lose along the way.”
While a healthy guy’s risks are much lower than a sick or old person’s, they’re not zero, Powell stresses.
You’re Not Contagious—but Your Fridge Might Be
Apart from mothers shifting the bacteria to their fetuses, human-to-human Listeria transmission isn’t a thing.
So even if you’re carrying around the infection, you’re not going to give it to your wife or sick parent, Powell says. But if you’re exposed to enough Listeria to become infected, that could mean the people you love are at risk, too. That’s because, presumably, they’re eating some of the same foods you are.
One thing you have to worry about: Your fridge.
While normal refrigerator temps are low enough to control the spread of other illness-causing bacteria, that’s not the case for Listeria, according to a paper in the Canadian Medical Association Journal.
Powell backs this up, and says once your fridge is contaminated, it’s only a matter of days before many ready-to-eat foods become contaminated.
He mentions milk, cheese, deli or smoked meats, and produce as food items you really want to eat soon after opening.
And don't let a "sell by" or "best by" date create false security. Those mostly refer to how long a retailer can keep selling customers an unopened item. “Once you open one of these, you want to eat it within 3 days,” he says. After that, toss it.
Also, keep any deli meats or cheeses in a drawer away from your fresh fruits and vegetables. And always keep food in containers—not on a plate out in the open refrigerator air.
More Ways to Protect Yourself From Listeria
While you might hear or read about major outbreaks—the ones that affect big commercial food sellers that send their stuff to multiple states—smaller listeriosis flares don’t always make the news. The FDAs safety alert site provides details on every known listeria hotspot.
Also: “Cook your food,” Powell advises.
Even light cooking kills Listeria. If you’re preparing foods yourself—as opposed to buying ready-to-eat products—you’re minimizing your risks.
Just be sure to cook your meat all the way through. Powell recommends buying a meat thermometer, and making sure you cook your proteins enough to satisfy the USDA’s safe minimum temperature guidelines.
What Happens If You Get Listeria?
“Interventions don’t work too well,” Powell says. “It’s best to avoid it, because once you have it there’s not much you can do but ride it out.”
If you’re suffering all those above symptoms and you think Listeria might be the cause, you should still see a doctor. In some cases, antibiotics may help, he says.
More importantly, your doctor can figure out if Listeria is really the cause of your illness. If you have listeriosis, your doc can help you protect the people you love, and put out a public health warning so others aren’t exposed.