Investigation Details
Posted April 4, 2022
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.
CDC investigated this outbreak in 2019 and 2020 but was unable to gather enough data to identify the source in the past. CDC reopened the investigation in November 2021 when four new illnesses were reported since the end of August 2021.
During the most recent investigation, epidemiologic, laboratory, and traceback data showed that packaged salads produced by Dole made people sick.
As of April 4, 2022, this outbreak is over.
Epidemiologic Data
A total of 18 people infected with the outbreak strain of Listeria monocytogenes were reported from 13 states (see map). The true number of sick people in an 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.
Illnesses started on dates ranging from August 16, 2014, to January 15, 2022 (see timeline). Sick people ranged in age from 50 to 94 years, with a median age of 76, and 83% were female. Of 16 people with information available, all were hospitalized. Three deaths were reported, one each from Michigan, Ohio, and Wisconsin.
State and local public health officials interviewed people (or their family) about the foods they ate in the month before they got sick. Of the 10 people interviewed, 9 (90%) reported eating packaged salads. Of the three people who remembered a specific brand, two reported Dole and one reported Little Salad Bar.
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 were closely related genetically. This suggests that people in this outbreak got sick from the same food.
In October 2021, before the most recent CDC investigation began, the Georgia Department of Agriculture identified Listeria in a Dole brand garden salad as part of a routine sampling program of food at grocery stores. WGS later showed that the Listeria in the garden salad was the outbreak strain. The garden salad was produced at Dole’s Bessemer City, North Carolina, facility.
After CDC reopened this outbreak investigation, the Michigan Department of Agriculture and Rural Development collected samples of packaged salads from retail stores for testing and identified the outbreak strain of Listeria in a Marketside brand package of shredded iceberg lettuce. The shredded iceberg lettuce was produced at Dole’s Yuma, Arizona, facility.
Dole conducted a root cause analysisexternal icon and collected samples from their facilities and equipment for testing. Dole found Listeria on equipment used to harvest iceberg lettuce. FDA conducted WGS and found that the Listeria on the equipment was the outbreak strain.
Dole’s continued investigation found the outbreak strain on a piece of equipment in their Yuma facility and in packaged salads on hold that were included in the initial recall.
Public Health Actions
On December 22, 2021, Dole recalledexternal icon all Dole-branded and private label packaged salads processed at their Bessemer City, North Carolina, and Yuma, Arizona, facilities.
On January 7, 2022, Dole recalledexternal icon additional products containing iceberg lettuce harvested by the contaminated harvesting equipment.
Epidemiologic, laboratory, and traceback data show that packaged salads produced by Dole are contaminated with Listeria and making people sick.
Epidemiologic Data
Since the last update on December 22, 2021, one more illness has been reported. As of February 1, 2022, 17 people infected with the outbreak strain of Listeria monocytogenes have been reported from 13 states (see map). Illnesses started on dates ranging from August 16, 2014, to December 30, 2021 (see timeline).
Sick people range in age from 50 to 94 years, with a median age of 75, and 82% are female. Of 15 people with information available, 13 have been hospitalized. Two deaths have been reported from Michigan and Wisconsin.
The true number of sick people in an 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.
State and local public health officials are interviewing people, or their family, about the foods they ate in the month before they got sick. Of the 9 people interviewed, 8 (89%) reported eating packaged salads. Of the three people who remembered a specific brand, two reported Dole and one reported Little Salad Bar.
Laboratory Data
Dole collected samples from their facilities and equipment for testing and found Listeria on equipment used to harvest iceberg lettuce. FDA conducted whole genome sequencing and found that the Listeria on the equipment was the outbreak strain.
Public Health Actions
On January 7, 2022, Dole recalledexternal icon additional products containing iceberg lettuce harvested by the contaminated equipment.
Do not to eat, sell, or serve any recalled products.
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.
CDC investigated this outbreak in 2019 and 2020 but was unable to gather enough data to identify the source in the past. CDC reopened the investigation in November 2021 when four new illnesses were reported since the end of August 2021.
Epidemiologic and recent laboratory data show that packaged salads produced by Dole are contaminated with Listeria and making people sick.
Epidemiologic Data
As of December 17, 2021, 16 people infected with the outbreak strain of Listeria monocytogenes have been reported from 13 states (see map). Illnesses started on dates ranging from August 16, 2014, to October 17, 2021 (see timeline).
Sick people range in age from 50 to 94 years, with a median age of 76, and 81% are female. Of 14 people with information available, 12 have been hospitalized. Two deaths have been reported from Michigan and Wisconsin.
The true number of sick people in an 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.
State and local public health officials are interviewing people, or their family, about the foods they ate in the month before they got sick. Of the 8 people interviewed, 7 (88%) reported eating packaged salads. Of the three people who remembered a specific brand, two reported Dole and one reported Little Salad Bar.
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 October 2021, the Georgia Department of Agriculture identified the outbreak strain of Listeria in a Dole brand garden salad as part of a routine sampling program of food at grocery stores. As a result, Dole recalledexternal icon some of their garden salad products that are now past their “best if used by” dates. This sampling was not part of this outbreak investigation, but WGS later showed that the Listeria bacteria in the garden salad were closely related to the outbreak strain.
After CDC reopened this outbreak investigation, Michigan Department of Agriculture and Rural Development collected samples of packaged salads from retail stores for testing and identified the outbreak strain of Listeria in a Marketside brand package of shredded iceberg that was produced by Dole.
Public Health Actions
On December 22, 2021, Dole recalledexternal icon all Dole-branded and private label packaged salads processed at the two facilities that produced the contaminated packaged salads.
Do not to eat, sell, or serve any recalled products. Investigators are working to determine if additional products may be contaminated.
