The multistate outbreak of Listeria monocytogenes infections linked to Dole packaged salads was the sixth largest in 2016. That outbreak sickened 19 people in the United States and caused one death in Michigan. All nineteen of the patients were hospitalized. In Canada, 14 people were sickened by these salad products. One of those patients died, although health officials have not determined if listeriosis was the cause of that death.
In March 2016, Food Poisoning Bulletin was the first to report that Dole knew about Listeria monocytogenes contamination in the plant in Springfield, Ohio, years before this outbreak. We requested information from the FDA through a Freedom of Information Act Report.
The company found the pathogenic bacteria in that plant in early 2014 and “infrequently” before that. The records date back to a 2012 inspection triggered by a recall for Listeria. FDA inspectors found that the plant was not constructed in a way that it could have been kept clean. Once Listeria monocytogenes is established in a facility, especially one that uses a lot of water, it can be very difficult to eradicate.
Whole genome sequencing performed on isolates from all 19 persons sickened in this country showed that the isolates were closely related genetically. Epidemiologic and lab evidence indicated that packaged salads produced at the Dole facility in Springfield, Ohio and sold under various brand names were the likely source of this outbreak. Dole voluntarily recalled all salad mixes produced in that plant on January 27, 2016.
Public health investigators used the PulseNet system to identify illnesses that may have been part of this outbreak. The case count by date was: Connecticut (1), Indiana (1), Massachusetts (1), Michigan (4), Missouri (1), New Jersey (1), New York (6), Ohio (2), and Pennsylvania (1). Ill persons ranged in age from 3 years to 83. One of the illnesses was in a pregnant woman.
All of the ill persons in Canada were infected with the same outbreak strain of Listeria monocytogenes. Whole genome sequencing showed that the isolates from those patients were closely related genetically to Listeria isolates from ill persons in the U.S.
Of the 14 ill people interviewed in this outbreak, 13, or 93%, said they ate a packaged salad the month before they got sick. All of the nine ill people who specified a brand of packaged salad said they ate Dole brand packaged salads. This outbreak was the first Listeria monocytogenes outbreak in this country linked to leafy greens.
The Ohio Department of Agriculture collected a Dole brand Field Greens packaged salad from a retail location and isolated Listeria monocytogenes bacteria. Whole genome sequencing showed that the Listeria isolate from the packaged salad was closely related genetically to isolates from ill people. The Public Health Agency of Canada also confirmed the presence of Listeria in packaged salads produced at the Dole Springfield, Ohio facility.
In April 2016, the U.S. Department of Justice launched an investigation into this outbreak. We are still waiting to see what the results of that investigation will be.