CDC is 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, 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 eight people infected with the outbreak strains of Listeria have been reported from three 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 specimens were collected from September 13, 2013 to March 28, 2016. Two 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 range in age from 56 years to 86, with a median age of 76. Seventy-five percent of ill people are female. All eight (100%) ill people were hospitalized, including one from Maryland and one from Washington who died, although listeriosis was not considered to be a cause of death for either person.
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 of the Outbreak
Epidemiologic and laboratory evidence available at this time indicates that frozen vegetables produced by CRF Frozen Foods of Pasco, Washington and sold under various brand names are one likely source of illnesses in this outbreak. This is a complex, ongoing investigation, and updates will be provided when more information is available.
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. Three of eight ill people, or their caregiver, were interviewed using a questionnaire that asked about a variety of foods. Two of these three people reported buying and eating frozen vegetables in the month before illness began and both reported Organic by Nature brand frozen vegetables. Organic by Nature 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 were produced by CRF Frozen Foods. Whole genome sequencing showed that the Listeria isolate from the frozen corn was closely related genetically to seven 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.
On April 23, 2016, CRF Frozen Foods recalled 11 frozen vegetable products because they may be 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. Recalled items were sold in plastic bags under various brand names, nationwide and in Canada. A full list of recalled products is available on the FDA 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.
Investigations are ongoing to determine if food sources used to manufacture CRF Frozen Foods products could explain some of the illnesses. CDC and state and local public health partners are continuing laboratory surveillance through PulseNet to identify additional ill people and to interview them.