Introduction

CDC collaborated 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 used the PulseNet system to identify illnesses that may have been part of this outbreak. PulseNet, coordinated by CDC, is the national subtyping network of public health and food regulatory agency laboratories. PulseNet performs DNA fingerprinting 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.

A total of nine people infected with the outbreak strains of Listeria were reported from four states since September 13, 2013. A list of states and the number of cases in each can be found on the Case Count Map page.

Listeria positive specimens were collected from September 13, 2013, to May 3, 2016. Three illnesses were reported in 2016. The remaining six illnesses reported during 2013-2015 were identified through a retrospective review of the PulseNet database. Ill people ranged in age from 56 to 91 years, with a median age of 76. Seventy-eight percent of ill people were female. All nine (100%) ill people were hospitalized, including three people who died. Listeriosis was considered to be a cause of death for one person in Connecticut. For the two deaths in Maryland and Washington, listeriosis was not considered to be a cause of death.

The outbreak can be illustrated with a chart showing the number of people who were diagnosed each month. This chart is called an epidemic curve or epi curve.

Investigation Summary

Epidemiologic and laboratory evidence indicated that frozen vegetables produced by CRF Frozen Foods of Pasco, Washington and sold under various brand names were a likely source of illnesses in this outbreak.

This outbreak was identified in March 2016. State and local health departments attempted to interview the ill people, a family member, or a caregiver for the ill person about the foods the ill person may have eaten in the month before the illness began. Four of nine ill people, or their caregiver, were interviewed using a questionnaire that asked about a variety of foods. Three of these four people reported buying and eating frozen vegetables in the month before illness began and two reported Organic by Nature brand frozen vegetables. The third ill person reported eating O Organic brand frozen vegetables. Both Organic by Nature and O Organic frozen vegetables are produced by CRF Frozen Foods.

During the same time period, as part of a routine product-sampling program, the Ohio Department of Agriculture collected packages of frozen vegetable products from a retail location and isolated Listeria from True Goodness by Meijer brand frozen organic white sweet cut corn and from True Goodness by Meijer brand frozen organic petite green peas. Both products are produced by CRF Frozen Foods. Whole genome sequencing (WGS) showed that the Listeria isolate from the frozen corn was closely related genetically to eight bacterial isolates from ill people, and the Listeria isolate from the frozen peas was closely related genetically to one isolate from an ill person. This close genetic relationship provides additional evidence that some people in this outbreak became ill from eating frozen vegetables produced by CRF Frozen Foods.

Also, FDA collected environmental samples from Oregon Potato Company, located in Pasco, Washington and isolated Listeria from these samples. WGS showed that the Listeria found in these environmental samples was closely related genetically to eight isolates from ill people in this outbreak. Based on this information, Oregon Potato Company voluntarily recalled wholesale onion products made in their facility, which led to multiple recalls of products sold at retail under many brand names that contained recalled onions.

On April 23, 2016, CRF Frozen Foods recalled 11 frozen vegetable products because they may have been contaminated with Listeria. On May 2, 2016, CRF Frozen Foods expanded the initial recall to include all organic and traditional frozen vegetable and fruit products processed in its Pasco, Washington facility since May 1, 2014. More than 350 consumer products sold under 42 separate brands were recalled, as well as at least 100 other products from other companies that contained recalled ingredients from CRF Frozen Foods. State health departments collected recalled products from ill people in California and Idaho and isolated an outbreak strain of Listeria in these product samples. Recalled items were sold under various brand names, nationwide and in Canada. A full list of recalled products is available on the FoodSafety.gov website. CDC recommends that consumers do not eat, and restaurants and retailers do not serve or sell, recalled organic and traditional frozen vegetables and fruit products and recalled products that contain these items.

This outbreak investigation is over. However, people could continue to get sick because recalled products may still be in freezers and people who don’t know about the recalls could eat them. Retailers should not sell and consumers should not eat recalled products. Read the Recall and Advice to Consumers and Retailers.

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