Federal officials have declared that a deadly outbreak of Listeria monocytogenes infections traced to Dole packaged salads has ended.

The most recent patient to be reported became sick on Jan. 15. It can take up to 70 days for symptoms of Listeria infections to appear, but the implicated salad was recalled in October and December 2021 and early January 2022 and had reached its expiration date before January, so officials believe patient counts have stabilized.

The Food and Drug Administration reported on April 4 that the patient count as of that day was 18 people in 13 states. Sixteen people required hospitalization and three people died. States with patients were Iowa, Idaho, Maryland, Michigan, Minnesota, North Carolina, Nevada, Ohio, Oregon, Pennsylvania, Texas, Utah and Wisconsin.

The states where the implicated salad was distributed were Alabama, Arizona, California, Colorado, Connecticut, Florida, Georgia, Hawaii,  Iowa, Idaho, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maine, Maryland, Michigan, Minnesota, Missouri, Mississippi, North Carolina, North Dakota, Nebraska, Nevada, New York, Ohio, Oklahoma, Oregon, Pennsylvania, South Carolina, Tennessee, Texas, Virginia, Washington and Wisconsin. The salad may have been further distributed to other states, according to the FDA.

Recalls related to the outbreak began in October 2021 when routine retail sampling by the Georgia Department of Agriculture found Listeria monocytogenes in prepackaged salad mix from a grocery store, according to the FDA.

“FDA conducted WGS (whole genome sequencing) analysis of an isolate shared by Dole, and the results confirmed that this isolate of Listeria matched the strain causing illness in this outbreak and also matched the strain of Listeria found in a positive product sample collected by the Michigan Department of Agriculture and Rural Development, as reported on Dec. 23, 2021,” according to the FDA’s outbreak update on April 4.

During investigation of the outbreak the company found contaminated equipment at its facilities.

“FDA sent investigators to multiple Dole processing facilities to conduct on-site inspections and Dole conducted a root cause analysis of their own in an effort to determine the potential source of contamination for this outbreak. Continued investigation conducted by Dole detected the presence of Listeria on a piece of equipment in their Yuma, AZ, facility,” according to the FDA.

“(Also) Dole detected the presence of Listeria monocytogenes on equipment used in the harvesting of the iceberg lettuce that was also used in finished products processed in the Dole Springfield, OH, and Soledad, CA, facilities. This finding prompted a subsequent voluntary recall on January 7, 2022.

FDA analyzed the positive samples collected by Dole from the harvesting equipment. Results from FDA’s whole genome sequencing (WGS) analysis showed that the strain of Listeria found on the harvesting equipment matched the strain causing illnesses in this outbreak. Dole decommissioned the harvester and it was later dismantled. Product on hold that was included in the December 2021 recall was later tested by Dole and tested positive for the strain of Listeria monocytogenes that caused illnesses in this outbreak.”

During the investigation, operations at the Bessemer City, NC, and Yuma, AZ, facilities were temporarily stopped for deep cleaning, sanitization, and verification swabbing, and have since resumed, the FDA reported.  

The FDA recommends that anyone who received recalled products use extra vigilance in cleaning and sanitizing any surfaces and containers that may have come in contact with these products to reduce the risk of cross-contamination. Listeria can survive in refrigerated temperatures and can easily spread to other foods and surfaces. It can live for months or years under refrigeration or freezing.

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