Outbreak Summary

Introduction

CDC collaborated with public health officials in several states and the U.S. Food and Drug AdministrationExternal (FDA) to investigate a multistate outbreak of Listeria monocytogenes infections (listeriosis). Listeria can cause a serious, life-threatening illness.

Public health investigators used the PulseNet system to identify illnesses that may have been 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). CDC PulseNet manages a national database of these DNA fingerprints to identify possible outbreaks. WGS gives a more detailed DNA fingerprint than PFGE.

A total of 19 people infected with the outbreak strain of Listeria were reported from nine states. A list of states and the number of cases in each can be found on the Case Count Map page.

Listeria specimens were collected from July 5, 2015 to January 31, 2016. Ill people ranged in age from 3 years to 83, and the median age was 64. Of ill people, 74% were female. All 19 (100%) ill people were reported as hospitalized, and 1 person from Michigan died as a result of listeriosis. One of the illnesses reported was in a pregnant woman. WGS was performed on Listeria isolates from all 19 ill people and showed that the isolates were closely related genetically. This close genetic relationship means that people in this outbreak were more likely to share a common source of infection, such as a contaminated food.

According to the Public Health Agency of CanadaExternal , ill people in Canada were infected with the same outbreak strain of Listeria. Whole genome sequencing of clinical isolates from ill people in Canada showed that the isolates were closely related genetically to Listeria isolates from ill people in the United States.

Investigation of the Outbreak

Epidemiologic and laboratory evidence indicated that packaged salads produced at the Dole processing facility in Springfield, Ohio and sold under various brand names were the likely source of this outbreak.

State and local health departments interviewed ill people about the foods they may have eaten or other exposures in the month before their illness began. Of 14 ill people who were asked about packaged salad, 13 (93%) reported eating a packaged salad. All of the 9 ill people who specified the brand of packaged salad eaten reported various kinds 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 closely related genetically to isolates from ill people. This information helped link the illnesses to Dole brand packaged salads produced at the Dole processing facility in Springfield, Ohio. Additionally, the Public Health Agency of Canada confirmed the presence of Listeria in packaged salads produced at the Dole Springfield, Ohio processing facility.

On January 21, 2016, Dole reported to CDC that it had stopped production at the processing facility in Springfield, Ohio and withdrew packaged salads from this facility that were on the market at that time. On January 27, 2016, Dole voluntarily recalledExternal all salad mixes produced in the Springfield, Ohio processing facility. The recall included several brands and varieties of salad mixes that were distributed throughout the United States and in Eastern Canada. The type of salad mixes produced at this facility were packaged in bags and plastic clamshell containers and were identified by the letter “A” at the beginning of the manufacturing code on the package. Any recalled salad mixes still on the market or in consumers’ homes would be past their expiration dates.

This outbreak appears to be over. More information about what to do with recalled fruits and vegetables is available on the Advice to Consumers, Restaurants, and Retailers page.