What is listeria? Things to know about the bacteria and how to prevent infection

BALTIMORE — At least two cases of listeria have been linked to ice cream in the Baltimore metro area, prompting health and safety concerns.

Listeria is a bacterium that can contaminate food and cause serious, sometimes fatal infections, particularly in pregnant women, newborns, the elderly and those with weakened immune systems, according to the Food and Drug Administration.

This month, a Baltimore County woman filed a lawsuit against a Pikesville supermarket and out-of-state ice cream manufacturers that she says sold products contaminated with listeria and led to the death of her newborn baby in 2023, according to a complaint filed in Baltimore County Circuit Court. She is seeking up to $30 million in damages.

Additionally, in May 2024, the FDA discovered listeria contamination during an inspection of ice cream manufacturer Totally Cool Inc.’s Owings Mills facility. This led to a nationwide recall of over 60 ice cream products from brands including Friendly’s, Hershey’s Creamery Corp. and Jeni’s. In March 2025, the FDA requested a permanent injunction against the company, which filed for bankruptcy after listeria was detected at one of its production lines during an unannounced inspection.

Last year, the Maryland Department of Health issued a consumer advisory for Boar’s Head ready-to-eat liverwurst and other deli meat products due to possible listeria contamination.

Below is information on listeria, how to prevent an infection, infection signs and symptoms and treatment.

What is listeria?

Listeria is a potentially dangerous bacterium that can contaminate various foods and cause serious illness, especially in vulnerable groups like young children, older adults and those with weakened immune systems. While rare, infections can be severe but are largely preventable with proper food safety practices, according to the Centers for Disease Control and Prevention.

“The thing about the bacteria that makes it problematic in terms of outbreaks is that it can grow at relatively cold temperatures as low as two degrees Celsius,” said Shmuel Shoham, a professor of clinical medicine in the Division of Infectious Diseases at the Johns Hopkins University School of Medicine. “So sometimes the bacteria can survive despite refrigeration, and then also the bacteria can form what are called biofilms, which allow it to survive in the environment.

“So you can have a situation where, unless meticulous hygiene measures are taken at a place where food is prepared, then it can get into the food and then survive in refrigeration.”

Here’s what the CDC says about listeria and how to reduce your risk of getting sick.

Risky foods

—Soft cheeses

—Hot dogs

—Cold cuts

—Unpasteurized milk products

—Pre-cut fruits and vegetables

—Raw shellfish and seafood

Shoham said there is one type of food that seems to have a “predilection” for contamination and infection: soft cheeses.

“Oftentimes, soft cheeses are made in ma-pa types of facilities and they may not have the ability to have the hygiene that a big industrial operation has,” Shoham said.

Symptoms of listeria infection

—Fever

—Muscle aches

—Nausea

—Diarrhea

According to Shoham, most people who get a listeria infection get gastroenteritis.

“Most of those go undiagnosed because we don’t typically test for listeria from stool, and they get better without specific therapy,” Shoham said.

“Pregnant women, highly immunocompromised people, people of big streams of age, they can get both gastroenteritis, but they can also get something more severe, either a cholesterol infection or rarely but dangerously essential nervous system infection.”

Highest risk of infection

—Pregnant women

—Newborns

—Adults aged 65 or older

—People with weakened immune systems

“The people at highest risk for listeria infection are going to be people that are pregnant, people that are immune-compromised, extremes of age, very young and very old,” Shoham said. “So for those people, particularly pregnant women, we tell them all kinds of foods not to eat. The reason we’re telling them that one of them is so that they do not get listeria. And if a pregnant woman gets listeria, she may get a bloodstream infection with it, and then, then they put the health of the unborn baby in danger.”

Treatment

—Fluids, especially for symptoms of diarrhea, to prevent dehydration

—Antibiotics

—Erythromycin, or trimethoprim-sulfamethoxazole for those with penicillin allergies

According to Shoham, most people will not need treatment.

“Most people will have a self-limited gastrointestinal syndrome, diarrhea, usually,” Shoham said. “ However, people who are at high risk, those people will typically be treated with amoxicillin or another drug called trimethoprim-sulfamethoxazole or bactrim.”

Prevention

—Know the foods likely to be contaminated

—Choose safer food options

—Clean, separate, and then cook

—Stay up to date on foodborne outbreaks and food recalls

“If you thoroughly cook animal-sourced food, if you thoroughly wash raw vegetables, if you avoid unpasteurized milk, especially unpasteurized soft cheeses,” Shoham said. “And then also smoked seafood, meat spreads, pates, cold cuts, hot dogs … those can all be particularly if they’re undercooked.

“Occasionally, there is an outbreak that happens with a specific kind of food. Once the CDC or the health authorities are on top of it, they tell you not to have that. So, occasionally, we’ll find out a certain ice cream brand or other food is associated with listeria. So those are the ways to avoid it.”