Since September 2015, CDC has been collaborating with public health officials in several states and the U.S. Food and Drug Administration (FDA) to investigate a multistate outbreak of Listeria monocytogenes infections (listeriosis). Listeria can cause a serious, life-threatening illness.
Public health investigators are using the PulseNet system to identify illnesses that may be part of this outbreak. PulseNet is the national subtyping network of public health and food regulatory agency laboratories coordinated by CDC. DNA “fingerprinting” is performed on Listeria bacteria isolated from ill people by using techniques called pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS). PulseNet manages a national database of these DNA fingerprints to identify possible outbreaks. WGS gives a more detailed DNA fingerprint than PFGE.
Twelve people infected with the outbreak strain of Listeria have been reported from six states since July 5, 2015. The number of ill people reported from each state is as follows: Indiana (1), Massachusetts (1), Michigan (4), New Jersey (1), New York (4), and Pennsylvania (1). WGS has been performed on clinical isolates from all 12 ill people and has shown that the isolates are highly related genetically.
Listeria specimens were collected from July 5, 2015 to December 23, 2015. Ill people range in age from 3 years to 83, and the median age is 66. Sixty-nine percent of ill people are female. All 12 (100%) ill people reported being hospitalized, including one person from Michigan who died as a result of listeriosis. One of the illnesses reported was in a pregnant woman.
The outbreak can be illustrated with a chart showing the number of people who were diagnosed each week. This chart is called an epidemic curve or epi curve.
Investigation of the Outbreak
Epidemiologic and laboratory evidence available at this time indicates that packaged salads produced at the Dole processing facility in Springfield, Ohio and sold under various brand names are the likely source of this outbreak.
State and local health departments are interviewing ill people about the foods they may have eaten or other exposures in the month before their illness began. Of five ill people who were asked about packaged salad, all five (100%) reported eating a packaged salad. Two (100%) of two ill people who specified the brand of packaged salad eaten reported various varieties of Dole brand packaged salad.
As part of a routine product sampling program, the Ohio Department of Agriculture collected a Dole brand Field Greens packaged salad from a retail location and isolated Listeria. This packaged salad was produced at the Springfield, Ohio Dole processing facility. In January 2016, WGS showed that the Listeria isolate from the packaged salad was highly related genetically to isolates from ill people. This information linked the illnesses to Dole brand packaged salads produced at the Dole processing facility in Springfield, Ohio.
On January 21, 2016, Dole reported to CDC that it had stopped production at the processing facility in Springfield, Ohio. The company also reported that it is withdrawing packaged salads currently on the market that were produced at this facility. The withdrawal does not affect other Dole products.
CDC recommends that consumers do not eat, restaurants do not serve, and retailers do not sell packaged salads produced at the Dole processing facility in Springfield, Ohio. These packaged salads were sold under various brand names, including Dole, Fresh Selections, Simple Truth, Marketside, The Little Salad Bar, and President’s Choice Organics. The packaged salads can be identified by the letter “A” at the beginning of the manufacturing code found on the package. At this time, there is no evidence to suggest that packaged salads produced at other Dole processing facilities in the United States are linked to illness.
CDC and state and local public health partners are continuing laboratory surveillance through PulseNet to identify additional ill people and to interview them. Updates will be provided when more information is available.