The Mystery of the Listeria That Lurked in Bags of Dole Salad

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Fresh Vegetables has voluntarily withdrawn all of its Dole-branded and private label packaged salads processed at the Springfield, Ohio plant in the wake of a listeria outbreak. (Courtesy of the FDA)

Last summer, cases of particular strain of Listeria started popping up in six states in the Northeast and Midwest U.S.

The Centers for Disease Control and Prevention says since July 2015, 12 people have been sickened and one person from Michigan has died in this outbreak. And the agency recently confirmed that five of the people who got sick reported eating packaged salad. Two of them specified that they ate Dole brand packaged salad.

Why are investigators only connecting the dots between the outbreak and its source?

Well, it wasn't until last week that DNA "fingerprinting" tests on a bag of salad greens packaged at a Dole facility in Springfield, Ohio conducted by the Ohio Department of Agriculture came back. The lab tests "showed that the Listeria isolate from the packaged salad was highly related genetically to isolates from ill people," according to a CDC release.

Dole Fresh Vegetables told the Food and Drug Administration on Friday it was temporarily suspending operations at the Springfield processing facility. The company also voluntarily withdrew from the market all of its Dole-branded and private label packaged salads processed at that location. (They include Fresh Selections, Simple Truth, Marketside, The Little Salad Bar and President's Choice Organics brands.)


Each year in the U.S., the CDC estimates that 1,600 people get sick from Listeria infections and 260 people die.

As the CDC notes, pregnant women, elderly people and those with compromised immune systems are most at risk. The CDC says at least 90 percent of people sickened by Listeria infections are in one of these higher-risk categories. In this outbreak, the mean age of the people who got sick is 66.

Meanwhile, some healthy people who are exposed to the bacteria never end up getting sick – or have just minor symptoms.

So, how do the guts of healthy people help fend off dangerous bacteria such as listeria? As we reported a few years back, the immune system of healthy people can protect against pathogens. Soon after Listeria invade our gut, white blood cells are dispatched to the scene. Each one acts as a little foot soldier battling it out with the bacteria.

For those who are infected, symptoms may include a fever, muscle aches and a stiff neck.

Copyright 2016 NPR.