Investigation Details
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 data showed that leafy greens were a likely source of the outbreak. However, there was not enough other data to identify a specific type or producer of leafy greens.
As of June 13, 2023, this outbreak is over.
Epidemiologic Data
As of June 13, 2023, a total of 19 people infected with the outbreak strain of Listeria were reported from 16 states (see map). Sick people’s samples were collected from July 3, 2018, to March 31, 2023 (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.
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 96 years, with a median age of 72, and 63% were female. Among 19 people with race information available, 17 people were White, 1 was African American/Black, and 1 reported “Other” race. Among 19 people with ethnicity information available, two people were Hispanic. Eighteen people were hospitalized, and no deaths were reported.
State and local public health officials interviewed people about the foods they ate in the month before they got sick. Of 14 people who answered questions about leafy greens, 13 (93%) people ate leafy greens, 13 (93%) ate iceberg lettuce, and 10 (71%) ate romaine lettuce. Twelve (86%) people ate packaged salads.
CDC conducted a case-case analysis, comparing foods that sick people in this outbreak reported eating to foods that people sick with Listeria reported eating who were not part of an outbreak. The analysis showed that people in this outbreak were 8 times more likely to eat iceberg lettuce (p=0.035), 5 times more likely to eat romaine lettuce (p=0.038), and 4 times more likely to eat packaged salads (p=0.049) than sick people not in this outbreak. This suggests that leafy greens were a likely source of this outbreak.
Three people ate leafy greens at the long-term care facilities they lived in, and one person ate leafy greens at a hospital they worked in. People bought leafy greens and different brands of packaged salads from several stores.
Laboratory 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 were closely related genetically. This suggests that people in this outbreak got sick from the same food.
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.
A specific food item has not yet been identified as the source of this outbreak.
Epidemiologic Data
As of February 14, 2023, a total of 11 people infected with the outbreak strain of Listeria have been reported from 10 states (see map). Sick people’s samples were collected from July 3, 2018, to January 31, 2023 (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.
Sick people range in age from 47 to 88 years, with a median age of 73, and 73% are female. Race or ethnicity information is available for ten sick people. One sick person reported Hispanic ethnicity. Of nine people that did not report Hispanic ethnicity, eight are White and one is African American/Black. Of ten people with information available, all have been hospitalized. No deaths have been reported.
State and local public health officials are interviewing people to find out what foods they ate in the month before they got sick.
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.
Public Health Actions
CDC advises people who are pregnant, aged 65 or older, or have a weakened immune system to contact their healthcare provider if they have any Listeria symptoms.
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.
A specific food item has not yet been identified as the source of this outbreak.
Epidemiologic Data
As of February 14, 2023, a total of 11 people infected with the outbreak strain of Listeria have been reported from 10 states (see map). Sick people’s samples were collected from July 3, 2018, to January 31, 2023 (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.
Sick people range in age from 47 to 88 years, with a median age of 73, and 73% are female. Race or ethnicity information is available for ten sick people. One sick person reported Hispanic ethnicity. Of nine people that did not report Hispanic ethnicity, eight are White and one is African American/Black. Of ten people with information available, all have been hospitalized. No deaths have been reported.
State and local public health officials are interviewing people to find out what foods they ate in the month before they got sick.
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.
Public Health Actions
CDC advises people who are pregnant, aged 65 or older, or have a weakened immune system to contact their healthcare provider if they have any Listeria symptoms.
