The Food and Drug Administration has begun traceback efforts related to a multi-state outbreak of infections from Listeria monocytogenes.

The source of the outbreak continues to be listed as unknown by the FDA even though it has begun product traceback.

According to the Centers for Disease Control and Prevention, there have been 11 people infected across 10 states. Ten of the patients have been so sick that they had to be admitted to hospitals. No deaths have been reported.

The outbreak is long-running with patients having been identified from July 2018 through January this year, according to the CDC. The patients range in age from 47 to 88 years old, with a median age of 73. One-fourth of the patients are female.

Public health officials are continuing to interview patients to find out what foods they ate in the weeks before becoming sick. It can take from several days up to more than two months for symptoms of Listeria infection to develop.

The patients have been identified and linked using whole genome sequencing, which provides DNA fingerprints of the bacteria. The patients’ samples have the same genetic signatures, which shows they are all part of a single outbreak.

The sick people live across the country, suggesting nationally distributed food. The patients live in Washington, California, Colorado, South Dakota, Missouri, Arkansas, Michigan, New York, Pennsylvania, and North Carolina.

Other ongoing outbreaks
Investigation continues in an outbreak of Salmonella Typhimurium infections linked to alfalfa sprouts. Fifteen people across three states have been confirmed as outbreak patients. Sick people live in South Dakota, Nebraska, and Oklahoma. Whole genome sequencing has linked the patients to a specific brand of sprouts sold in late December 2022 and early January 2023.

More people have likely been sickened, partly because some patients do not seek medical attention and others are not specifically tested for Salmonella infection, according to the CDC.

“FDA’s traceback investigation is ongoing but has identified Sun Sprouts brand alfalfa sprouts grown by SunSprout Enterprises of Fremont, NE, as a likely source of illnesses in this outbreak,” according to an FDA outbreak notice.

In another outbreak, the FDA has identified enoki mushrooms distributed by Utopia Foods Inc. of Glendale, NY, and imported from China, and enoki mushrooms labeled as “Producer: Shandong Youhe Biotechnology, Co.,” with an address in China and “Distributed By: Sun Hong Foods Inc.” as likely sources of Listeria monocytogenes infections. 

Enoki mushrooms are long thin white mushrooms, usually sold in clusters. They are especially popular in East Asian cuisine and are also known as enokitake, golden needle, futu, seafood, or lily mushrooms. There have been numerous recalls of a wide variety of brands of enoki mushrooms recalled in the United States in the past two years because of contamination with Listeria.

As of its most recent outbreak updat on Jan. 18, the CDC reported three patients included in this outbreak. Through ongoing import and product sampling of enoki mushrooms, two strains of Listeria monocytogenes detected on enoki mushroom products have been determined through Whole Genome Sequencing to be the same strains of Listeria monocytogenes linked to illnesses in this outbreak. Both strains are included in this outbreak investigation.

Additional sample collection and analysis conducted by the Maryland Department of Health have also identified both outbreak strains of Listeria monocytogenes in two product samples of enoki mushrooms. These products that tested positive have the following printed on their packaging “Producer: Shandong Youhe Biotechnology Co.,” with an address in China, and “Distributed By: Sun Hong Foods, Inc.”