In February 2023, the CDC announced a multistate outbreak of Listeria monocytogenes. The outbreak investigation was closed on June 13, 2023.

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. A total of 19 people infected with the outbreak strain of Listeria had been reported from 16 states. Sick people's samples were collected from July 3, 2018 to March 31, 2023. Eighteen people were hospitalized. No one died. There were no deaths. There was one pregnancy-associated illness in a newborn.

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.

Whole genome sequencing (WGS) showed the bacteria from sick people's samples were closely related genetically. Investigators concluded that this suggested that people in this outbreak got sick from the same food.