The CDC used a technique called whole genome sequencing to link the outbreak to Springfield.
DNA fingerprints were pulled from samples of listeria from ill patients, Fowlie said. Public health labs across the U.S. upload the DNA fingerprints to Pulsenet, and the CDC can then review data to see if something unusual or unexpected is happening, indicating a possible outbreak, Fowlie said.
Whole genone sequencing shows the complete genetic makeup of an organism, said Lauren Kotwicki, a spokeswoman for the U.S. Food and Drug Administration. She likened it to a construction project. Instead of a building’s outline, the technique can show the building’s entire blueprint, Kotwicki said.
“Because the technology allows the FDA to identify the cause of an outbreak more quickly, the FDA is able to apply it in ways that have the potential to help reduce food-borne illnesses and deaths over the long term both in the U.S. and abroad,” Kotwicki said.
In this case, the listeria samples taken from sick patients were genetically similar, Fowlie said. The Ohio Department of Health later took samples of packaged salads produced in Springfield and found they shared many genetic traits with the samples from patients.
“Also, epidemiologic evidence showed of five people who were asked about eating packaged salad, all five had reported eating packaged salads in the month before their illness began, and two of two people who remembered the brand of packaged salad eaten said Dole brand,” Fowlie said. “This epidemiologic and lab information linked the illnesses to Dole brand packaged salads produced at the Dole processing facility in Springfield, Ohio.”
Dole voluntarily closed its Springfield facility Thursday, after one death and 12 illnesses in several states. The CDC has been investigating the cases since September last year, but they were not linked to the Springfield production site until this month.
So far, no deaths or illnesses have been reported in Ohio, according to state and local health officials.
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