All eight were hospitalized, including one each from Maryland and Washington who died, although listeriosis was not a cause of death for either of them, said the Centers for Disease Control and Prevention (CDC).
Listeria specimens were collected from September 2013 to March 28 this year. Two illnesses were reported in 2016.
The remaining six were during 2013-2015 and were identified through a retrospective review of the PulseNet database.
Frozen veg implicated after patient questionnaire
The outbreak was identified in March this year. Health departments interviewed 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.
Organic and non-organic broccoli, butternut squash, carrots, cauliflower, corn, edamame, green beans, Italian beans, kale, leeks, lima beans, onions, peas, pepper strips, potatoes, potato medley, root medley, spinach, sweet potatoes, various vegetable medleys, blends, and stir fry packages, blueberries, cherries, cranberries, peaches, raspberries, and strawberries. For a full list go here
Two of these three 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 period, as part of routine product-sampling, the Ohio Department of Agriculture collected packages of frozen vegetable products from retail 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 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 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, said the CDC.
Product recall and Canada affected
In late April, CRF Frozen Foods recalled 11 frozen vegetable products due to potential Listeria contamination. CRF suspended operations at the facility on April 25.
This week it expanded the recall to include all organic and traditional frozen vegetable and fruit products processed in its Pasco, Washington facility since May 1, 2014.
A total of 358 consumer products sold under 42 separate brands have been recalled.
All affected products have best by dates or sell by dates between April 26, 2016 and April 26, 2018.
They may have been purchased in all fifty US states and Canadian Provinces: British Columbia, Alberta, Manitoba, and Saskatchewan.
Investigations are ongoing to determine which food source used to manufacture CRF Frozen Foods products could explain some of the illnesses, said the CDC.
Costco Wholesale Canada is recalling Organic by Nature brand frozen Organic Butternut Squash 2kg and Organic Vegetable Medley 2.5kg due to possible Listeria monocytogenes contamination.
The Canadian Food Inspection Agency (CFIA) said the move was triggered by the recall in the US but there have been no reported illnesses in the country.