The Dole Listeria outbreak evaded initial detection because leafy greens had never before been linked to a Listeria outbreak and were not included on food history questionnaires used in interviews of the first case patients, according to a new report from the Centers for Disease Control and Information (CDC). The deadly outbreak, linked to bagged salads produced at Dole’s plant in Springfield, Ohio and sold under a variety of brand names ended in April after sickening 33 people in the U.S. and Canada.
In the U.S., 19 people were sickened and one of them died, according to the CDC. In Canada, 14 people were sickened and three of them died, although health officials in Canada have not been determined if Listeria was the cause of those deaths. All case patients in both countries were hospitalized. One illness was reported in a pregnant woman.
Health officials first identified the outbreak in September 2015, using PulseNet, the national subtyping network used to monitor food poisoning. The cluster patients had been sickened by the same strain, with onset of illness reported on or after July 5, 2015. In November, health officials used a standard food history questionnaire to gather information about foods seven case patients had eaten in the weeks before becoming ill. The questionnaires did not include leafy greens and a food source was not identified.
Then, in December 2015 and January 2016, the case patients, now eight of them, were interviewed again, this time with open-ended questionnaires and shopper card records provided where available. This time there was a common food. All of them reported eating leafy greens all in the month before becoming ill.
Seven reported eating romaine, six reported eating spinach, six recalled eating packaged salads and three of them remembered brand names.
Coinciding with the second round of questionnaires were the results of tests performed on packages of Dole salad purchased at a grocery by the Ohio Department of Agriculture as part of a routine sampling program. The Listeria strain cultured from the salad was highly related to the clinical isolates. The salad was produced at Dole’s facility in Springfield, Ohio
On January 21, 2016, Dole halted production at the plant and conducted a market withdrawal of salads produced at the plant and sold under 22 brand names. On January 27, Dole issued a recall of the salads.
The outbreak marks the first time an outbreak of listeriosis was associated with leafy greens and the eighth time since 2008 that a Listeria outbreak was associated with fresh produce, according to the CDC.