Investigation Details
Posted April 7, 2023
CDC, public health and regulatory officials in several states, and the U.S. Food and Drug Administration (FDA) investigated a multistate outbreak of Listeria monocytogenes infections.
Epidemiologic, laboratory, and traceback data showed that enoki mushrooms imported from China made people sick.
As of April 7, 2023, this outbreak is over.
Epidemiologic Data
A total of five people infected with one of the outbreak strains of Listeria were reported from four states (see map). Sick people’s samples were collected from October 5, 2022, to February 3, 2023 (see timeline).
The true number of sick people in this outbreak is likely higher than the number reported, and the outbreak may not have been limited to the states with known illnesses. This is because some people recover without medical care and are not tested for Listeria.
Public health officials collected many different types of information from sick people, including their age, race, ethnicity, other demographics, and the foods they ate in the month before they got sick. This information provided clues to help investigators identify the source of the outbreak.
Sick people ranged in age from less than 1 to 63 years, with a median age of 43, and 60% were female. Three people were Asian and two were Hispanic. Of the two people who reported Hispanic ethnicity, one reported White and one reported “Other” race. All sick people were hospitalized, and no deaths were reported.
Two sick people reported eating enoki mushrooms or eating at restaurants with menu items containing enoki mushrooms. Three people did not report eating enoki mushrooms, but two of them reported shopping at grocery stores or eating at restaurants that sell Asian foods.
Laboratory and Traceback Data
Public health investigators used the PulseNet system to identify illnesses that were part of this outbreak. CDC PulseNet manages a national database of DNA fingerprints of bacteria that cause foodborne illnesses. DNA fingerprinting is performed on bacteria using a method called whole genome sequencing (WGS).
WGS showed that bacteria from sick people’s samples are closely related genetically. This suggests that people in this outbreak got sick from the same food.
In November 2021, FDA found Listeria in one sample of enoki mushrooms that they collected at import, as part of FDA’s strategy to prevent Listeria outbreaks linked to imported enoki mushrooms. These enoki mushrooms were destroyed. The Listeria from this sample was closely related genetically to the Listeria that made the people in this outbreak sick. However, the firm associated with this sample was not identified as a potential source of enoki mushrooms in this outbreak.
In November 2022, the Michigan Department of Agriculture and Rural Development collected enoki mushroom samples from a store where a sick person in this outbreak bought enoki mushrooms. They found Listeria in a sample of Green Day Produce brand enoki mushrooms. The Listeria found in this sample was not the outbreak strains and was not linked to any reported Listeria illness in the United States. On November 17, 2022, Green Day Produce recalled these enoki mushrooms due to Listeria contamination.
In December 2022, Missouri state officials found Listeria in a sample of Utopia Foods brand enoki mushrooms as part of routine retail sampling. Nevada state officials also found Listeria in Utopia Foods brand enoki mushroom samples that they collected from the supplier of a restaurant where a sick person ate. The Listeria found in the Utopia Foods samples was not the outbreak strains and was not linked to any reported Listeria illness in the United States. On December 13, 2022, Utopia Foods recalled these enoki mushrooms due to Listeria contamination. In January 2023, FDA found the outbreak strains of Listeria in an import sample of Utopia Foods brand enoki mushrooms. These enoki mushrooms were imported from China. On January 13, 2023, Utopia Foods expanded their recall of enoki mushrooms.
In December 2022, Missouri state officials found one of the outbreak strains of Listeria in a sample of enoki mushrooms produced by Shandong Youhe Biotechnology Co. In January 2023, Maryland Department of Health found both outbreak strains in two samples of enoki mushrooms produced by the same company in China.
Public Health Actions
Many samples of enoki mushrooms were found to be contaminated with various strains of Listeria, including the two outbreak strains. Enumeration (a way to measure how much Listeria is on a food) was conducted for some samples and large amounts of Listeria were found.
On January 13, 2023, Utopia Foods expanded their recall of enoki mushrooms after the outbreak strains were found in a sample. On January 27, 2023, FDA and CDC advised people not to eat enoki mushrooms produced by Shandong Youhe Biotechnology Co. after the outbreak strains were found in three samples.
Although this outbreak investigation has ended, CDC and FDA are working to understand the risk of Listeria contamination in enoki mushrooms.
While this assessment is ongoing, CDC advises:
- People who are pregnant, aged 65 or older, or have a weakened immune system should not eat raw enoki mushrooms.
- Cook enoki mushrooms thoroughly.
- Keep raw enoki mushrooms separate from foods that won’t be cooked.
- Wash your hands, items, and surfaces that have touched raw enoki mushrooms.
- Restaurants should cook enoki mushrooms thoroughly before serving to customers and keep raw enoki mushrooms separate from foods that won’t be cooked.
FDA added enoki mushrooms from China to a country wide import alert (Import Alert #25-21).
Laboratory Data
The Maryland Department of Health found the outbreak strains of Listeria in two samples of enoki mushrooms produced by Shandong Youhe Biotechnology Co., China.
Public Health Actions
Do not eat, sell, or serve recalled or contaminated enoki mushrooms. CDC also advises people who are pregnant, aged 65 or older, or have a weakened immune system to not eat any raw enoki mushrooms, even if they are not recalled. Instead, cook enoki mushrooms thoroughly before eating.
Epidemiologic and laboratory data show that enoki mushrooms are contaminated with Listeria and are making people sick.
FDA found two strains of Listeria in an import sample of Utopia Foods brand enoki mushrooms. One strain is linked to the two illnesses that were already included in this outbreak, and the other strain is linked to one additional illness. Both strains are now included in this outbreak investigation.
Epidemiologic Data
Since the last update on November 22, 2022, one more illness has been linked to this outbreak. As of January 18, 2023, three people infected with the outbreak strains of Listeria have been reported from three states (see map). Sick people’s samples were collected from October 3, 2022, to October 8, 2022 (see timeline).
The true number of sick people in this outbreak is likely higher than the number reported, and the outbreak may not be limited to the states with known illnesses. This is because some people recover without medical care and are not tested for Listeria. In addition, recent illnesses may not yet be reported as it usually takes 3 to 4 weeks to determine if a sick person is part of an outbreak.
Public health officials collect many different types of information from sick people, including their age, race, ethnicity, other demographics, and the foods they ate in the month before they got sick. This information provides clues to help investigators identify the source of the outbreak.
Sick people range in age from 30 to 56 years, with a median of 42 years, and 66% are male. Two people are Hispanic, and one person is Asian. All three have been hospitalized, and no deaths have been reported.
Two sick people reported eating enoki mushrooms or eating at restaurants with menu items containing enoki mushrooms. One patient did not report eating enoki mushrooms but reported shopping at various Asian grocery stores.
Laboratory Data
FDA found the outbreak strains of Listeria in an import sample of Utopia Foods brand enoki mushrooms.
Previously, in December 2022, Missouri state officials conducted routine sampling and found Listeria in a sample of Utopia Foods brand enoki mushrooms. The Listeria found in this sample was not the outbreak strains, and it was not linked to any reported Listeria illness in the United States. On December 13, 2022, Utopia Foods recalled these enoki mushrooms.
Public Health Actions
On January 13, 2023, Utopia Foods expanded their recall of enoki mushrooms.
Do not eat, sell, or serve recalled enoki mushrooms. CDC also advises people who are pregnant, aged 65 or older, or have a weakened immune system to not eat any raw enoki mushrooms, even if they are not recalled. Instead, cook enoki mushrooms thoroughly before eating.
Laboratory Data
The Michigan Department of Agriculture and Rural Development found Listeria in a sample of enoki mushrooms. These mushrooms were collected from a store where a sick person in this outbreak bought enoki mushrooms. The Listeria found in this sample is not the outbreak strain, and it is not linked to any reported Listeria illness in the United States. On November 17, 2022, Green Day Produce, Inc. recalled these enoki mushrooms due to Listeria contamination.
CDC, public health and regulatory officials in several states, and the U.S. Food and Drug Administration (FDA) are collecting different types of data to investigate a multistate outbreak of Listeria monocytogenes infections.
Epidemiologic and laboratory data show that enoki mushrooms contaminated with Listeria are making people sick. Investigators are working to identify specific brands of enoki mushrooms that may be linked to these illnesses.
Epidemiologic Data
As of November 15, 2022, two people infected with the outbreak strain of Listeria have been reported from two states (see map). Sick people’s samples were collected from October 5, 2022, to October 8, 2022 (see timeline).
The true number of sick people in this outbreak is likely higher than the number reported, and the outbreak may not be limited to the states with known illnesses. This is because some people recover without medical care and are not tested for Listeria. In addition, recent illnesses may not yet be reported as it usually takes 3 to 4 weeks to determine if a sick person is part of an outbreak.
Public health officials collect many different types of information from sick people, including their age, sex, other demographics, and the foods they ate in the month before they got sick. This information provides clues to help investigators identify the source of the outbreak.
The two sick people are 30 and 42 years old, and they are both males. Both have been hospitalized, and no deaths have been reported.
Both sick people reported eating enoki mushrooms or eating at restaurants with menu items containing enoki mushrooms.
Laboratory Data
Public health investigators are using the PulseNet system to identify illnesses that may be part of this outbreak. CDC PulseNet manages a national database of DNA fingerprints of bacteria that cause foodborne illnesses. DNA fingerprinting is performed on bacteria using a method called whole genome sequencing (WGS).
WGS showed that bacteria from sick people’s samples are closely related genetically. This suggests that people in this outbreak got sick from the same food.
In November 2021, FDA found Listeria in one sample of enoki mushrooms that they collected at import, as part of the FDA’s strategy to prevent Listeria outbreaks linked to imported enoki mushrooms. These enoki mushrooms were destroyed. The Listeria from this sample is closely related genetically to the Listeria that made the people in this outbreak sick. However, to date, the firm associated with this sample has not been identified as a potential source of enoki mushrooms in this outbreak.
Public Health Actions
CDC advises people who are pregnant, aged 65 or older, or have a weakened immune system to not eat raw enoki mushrooms. CDC also advises restaurants to not serve raw enoki mushrooms. Cook enoki mushrooms thoroughly to kill any foodborne germs.
Currently, FDA has issued three import alerts that include enoki mushrooms.
