An ongoing listeria outbreak in fresh, soft cheeses threatens 26 states on the East Coast and the Midwest, with at least four positive cases and one death in Maryland, according to the Centers for Disease Control and Prevention.

The source is believed to be a New Jersey-based company called El Abuelito Cheese Inc., which has recalled several varieties of its Mexican-style soft cheeses.

The U.S. Food and Drug Administration warned El Abuelito Cheese about the possibility of a listeria outbreak in a June 2020 letter after inspections revealed food safety violations at the company’s plant.

“During our inspection, FDA investigators found serious violations,” the FDA’s letter stated. The agency’s inspection had found non-harmful types of listeria but warned the cheese company that the presence of any type of listeria meant that conditions were ripe for listeria monocytogenes, which causes disease in humans.

“Listeria monocytogenes is a known or reasonably foreseeable hazard for cheese,” the FDA’s letter explained. “Sanitation controls are generally applied to prevent contamination… and environmental monitoring for listeria species is usually used to verify these controls.”

Eight months after the FDA issued its warning letter, the Centers for Disease Control and Prevention first published reports about a possible listeria outbreak in soft cheeses, listing seven known cases between October 2020 and February 2021.

At the time, the precise source of the outbreak was unknown, but investigators had already found a possible link to Hispanic-style fresh and soft cheeses.

By Feb. 16, Connecticut’s Department of Public Health had discovered a possible connection between El Abuelito Queso Fresco cheese and the listeria outbreak, which was announced by the CDC the next day.

Once this connection was confirmed, El Abuelito issued a recall for all queso fresco cheeses products with sell-by dates through Mar. 28, including those sold under the brand names El Abuelito, Rio Grande and Rio Lindo.

By the end of February, El Abuelito had expanded its recall to all queso fresco, quesillo, or requeson cheeses produced at the contaminated facility, according to the CDC’s timeline.

Eleven cases of listeria infections - 10 resulting in hospitalizations - were recorded by the CDC at this point: four cases in Maryland, four in New York, two in Virginia and one in Connecticut. In Maryland, there had been one death reported to the CDC.

The phone number provided by El Abuelito on the recall press release on the FDA website has been disconnected.

When the company was contacted by a different number, an employee who answered the call stated that the company is no longer producing cheese, and requested a phone number. There has been no further contact with El Abuelito.

Listeria on its own is generally not a significant cause of illness in the United States, according to Dr. Martin Wiedmann, co-director of the New York Integrated Food Safety Center of Excellence and professor of food safety at Cornell University.

Listeria infections primarily affect pregnant women, newborns, older adults, and people with weakened immune systems, according to the CDC.

In the United States, there are only about 1,600 known cases per year, but around 90% of those people end up in the hospital, Wiedmann said.

“Listeria is one of those organisms that generally causes severe disease,” including septicemia, which is blood poisoning, and meningitis, which is an infection of the brain, he said.

Wiedmann added that about a fourth of the listeria cases involving pregnant women cause abortions, between 300 and 400 annually.

The best way to avoid listeria infections, according to the CDC, is to:

# Avoid raw sprouts

# Avoid smoked fish

# Avoid cut melons that have been left at room temperature for more than four hours

# Avoid hot dogs, pâtés, lunch meats, and cold cuts that have not been cooked to an internal temperature of 165℉ or have been in the refrigerator longer than two weeks

# Avoid unpasteurized dairy products and soft cheeses such as queso fresco, queso blanco, brie and Camembert

# Keep the refrigerator temperature lower than 40℉ and the freezer lower than 0℉

“Use separate knives, utensils and boards for raw food versus cooked foods,” Wiedmann cautioned. “Don’t use the same spatula to put your burgers on the barbecue and then take off the finished burger, because you’re cross-contaminating it… Keep your food cold or keep it really hot. If it’s somewhere in the middle, it gets dangerous. That’s particularly important for listeria, because listeria can grow at refrigeration temperatures.”

For more information about avoiding a listeria infection, see the CDC’s “Question and Answers” page for listeria.

For more information about the El Abuelito listeria outbreak, see the CDC’s webpage called “Listeria Outbreak Linked to Queso Fresco Made by El Abuelito Cheese Inc.”